# Abbreviations and Acronyms

The Apple Style Guide entry on abbreviations and acronyms plus technical/industry acronym definitions.

## Entries

### abbreviations and acronyms
An acronym is a pronounceable word formed from the initial letter or letters of major parts of a compound term. An abbreviation is usually formed in the same way but isn't pronounced as a word. Abbreviations are often lowercase or a mix of lowercase and uppercase. Acronyms are almost always all caps, regardless of the capitalization style of the spelled-out form.

> Abbreviation: mph—for *miles per hour*; MB/s—for *megabytes per second*
> Acronym: ROM—for *read-only memory*

- *When to spell out:* If you think your audience might not be familiar with an abbreviation or acronym, spell out its first occurrence on a page or in a section. In user materials, spell out the term when you introduce it.
- *How to spell out:* When you spell out a term, generally put the spelled-out version first, with the abbreviation or acronym in parentheses.

> internet service provider (ISP)

If the abbreviation or acronym is much more familiar than the spelled-out version, you can put the abbreviation or acronym first, followed by the spelled-out version in parentheses, or you can explain that the abbreviation is "short for" the spelled-out version and place the spelled-out version in italics.

> You can share your personal URL (Uniform Resource Locator).
> An internet address is sometimes called a *URL*, short for *Uniform Resource Locator*.

- *File types:* Use all caps for abbreviations of file types.

> a JPEG file, an AIFF file, the MP3 file

Filename extensions, which indicate the file type, should be in lowercase.

> .jpg, .aif, .mp3, .iba

See also *filename extensions*; [file types](#file-types).

- *Pronunciation:* If you think the reader might not know how to pronounce the acronym, provide a pronunciation key.

> WYSIWYG (pronounced "WIZ-zee-wig")

See also *pronunciation*.

- *Articles:* Use the article *a* or *an* with an abbreviation or acronym, depending on its pronunciation.

> a SAN, a USB port, an FAQ, an LCD screen

- *Punctuation:* Don't use periods except in abbreviations for nonmetric units of measure and in the abbreviations *a.m.*, *p.m.*, and *U.S.* (see [U.S.](#us) for exception).
- *Plural:* Don't add an apostrophe before the *s* when you form the plural of an abbreviation.

> CDs, ICs, ISPs

- *Latin:* Avoid using Latin abbreviations.

> Correct: *for example*, *and others*, *and so on*, and *that is*, or equivalent phrases
> Incorrect: *e.g.* (for example), *et al.* (and others), *etc.* (and so on), *i.e.* (that is)

- *Units of measure:* See [Units of measure](units-of-measure.md) for detailed usage guidelines.
- *Product names:* Don't abbreviate any Apple product or service names, whether or not the product or service is trademarked or has a service mark.

### AAC
Abbreviation for *Advanced Audio Coding*, an industry-standard audio compression format. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### AC
Abbreviation for *alternating current*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### AFP
Abbreviation for *Apple Filing Protocol*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### ANSI
Acronym for *American National Standards Institute*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### APFS
Abbreviation for *Apple File System*, the default file system used to format Apple devices and external storage devices.

### API
Abbreviation for *application programming interface* (not *application program interface*). To refer to more than one API, use *APIs*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### APN
Abbreviation for *Access Point Name*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### APNs
Abbreviation for *Apple Push Notification service*, the service that Apple provides to allow developers to send push notifications. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms). See also [push notification](apple-features-software.md#push-notification).

### ASCII
Acronym for *American Standard Code for Information Interchange*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### ASIC
Acronym for *application-specific integrated circuit*. Note hyphen in the spelled-out version. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### AVCHD
Abbreviation for *Advanced Video Coding High Definition*, a high-definition digital video format for recording and playback. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### bit/s
Abbreviation for *bits per second*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### bps
Don't use as the abbreviation for *bits per second*. Use *bit/s*.

### CD
Abbreviation for *compact disc*. Use *disc*, not *disk*, to refer to CD media.

### CLUT
Acronym for *color lookup table*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### CPU
Abbreviation for *central processing unit*. Avoid in user materials; use *processor* to refer to the chip and use *computer* or *system* to refer to the computer itself. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms). See also *computer*; [processor](apple-features-software.md#processor); *system*.

### CR
Abbreviation for *carriage return*. Use only when you refer specifically to ASCII character $0D or its equivalent. Explain the term *carriage return* if your audience includes first-time computer users. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

Use *return character* when you write about, for example, searches for return characters. Use *Return key* for the key users press.

### Ctrl
Abbreviation for *Control*. Use the abbreviation only when space constraints don't allow use of the full term (as in column headings in tables); otherwise, use *Control*, as in *Control key* or *Control-S*. Don't use *CTRL*.

### DAC
Acronym for *digital-to-analog converter*. Note hyphenation in the spelled-out version. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### DIMM
Acronym for *dual inline memory module*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### dpi
Abbreviation for *dots per inch* (n.) and *dot-per-inch* (adj.). For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

> The printer provides a resolution of 600 dots per inch (dpi); it can be upgraded to 1200 dpi.
> The printer provides a 600-dot-per-inch (dpi) resolution; some printers offer 1200 dpi resolution.

### DRAM
Acronym for *dynamic random-access memory*. Pronounced "DEE-ram." For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### DRM
Abbreviation for *digital rights management*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### DV
An industry-standard video format. Generally, use *DV* to refer to the format or to products that use the format. Don't use *DV* to refer to the medium *digital video*. Related terms include *DV format*, *DV standard*, *DV camera*, *DV camcorder*.

### DVD
An optical disc designed for high-capacity storage. Use *disc*, not *disk*, to refer to DVD media.

### DVI
Abbreviation for *Digital Visual Interface*, not *Digital Video Interface*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### DVR
Abbreviation for *digital video recorder*. Use to refer to a device, such as a portable media player or set-top box, that records digital video to file-based media such as a hard disk or an optical disc. Don't use *DVR* when you mean *camcorder*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms). See also *camcorder*.

### EMI
Abbreviation for *electromagnetic interference*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### EU
No periods. OK to abbreviate or to spell out *European Union* as a noun. Use the abbreviation for the adjective form.

### FAQ
Abbreviation for *frequently asked questions*. *FAQ* is singular; use the article *an*. Use *FAQs* to refer to more than one set of frequently asked questions. Use title-style capitalization if the full term precedes a noun: *the Frequently Asked Questions document*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### fps
Abbreviation for *frames per second*. Include a space between the number and *fps*: *24 fps*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### FTP
Abbreviation for *File Transfer Protocol*. Avoid as a verb; use *transfer files* instead. The UNIX command `ftp` is all lowercase. In the term *anonymous FTP*, the *a* is lowercase. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

> Correct: You can use FTP software to transfer files from a remote computer to your computer.
> Correct: You use the `ftp` command to transfer files from a remote computer to your computer.
> Incorrect: You can FTP files from a remote computer to your computer.

### GIF
Acronym for *Graphics Interchange Format*, a bitmapped graphics file format that includes data compression. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms). See also *file format*.

### GPU
Abbreviation for *graphics processing unit*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### GUI
Acronym for *graphical user interface*. Don't use. Instead, use *interface* (in user materials) or *UI* (in developer materials).

### H.264
A video compression standard (or video codec). Also known as *MPEG-4 Part 10* and *AVC* (or *Advanced Video Coding*).

### HD (n., adj.)
Abbreviation for *high definition* (n.) and *high-definition* (adj.). For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### HDMI
Abbreviation for *High-Definition Multimedia Interface*. Related terms include *HDMI port*, *HDMI input*, *HDMI output*, *HDMI cable*, *HDMI to HDMI cable*, and *HDMI to DVI cable*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### HDR (n., adj.)
Abbreviation for *high dynamic range* (n.) and *high-dynamic-range* (adj.). A video or still-image format that allows additional levels of brightness per color component.

### HDV
A format for recording and playback of high-definition video on standard DV cassette tapes using a form of MPEG-2 compression. Don't use *HDV* to refer in general to high-definition video.

### HFS Plus
Not *HFS+*. The technical name for a file system used to format a disk for use with macOS. (*HFS* stands for *hierarchical file system*.) Avoid in user materials; use *Mac OS Extended format* instead.

### HFS Plus (Journaled)
Not *HFS+ (Journaled)*. Avoid in user materials; use *Mac OS Extended (Journaled) format* instead.

### HTML
Abbreviation for *Hypertext Markup Language*. Use lowercase when the abbreviation is part of a URL. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### HTTP
Abbreviation for *Hypertext Transfer Protocol*. Use lowercase when the abbreviation is part of a URL. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### HUD
Acronym for *heads-up display*, a window for making adjustments and selecting options in some apps. Precede *HUD* with *a*, not *an*. Avoid unless the term appears in the user interface. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### IEEE
Abbreviation for *Institute of Electrical and Electronics Engineers*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### IM
Abbreviation for *instant message*. Don't use; use *message*.

### IMAP
Acronym for *Internet Message Access Protocol*. Pronounced "eye-map." For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### IP
Abbreviation for *Internet Protocol*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### IrDA
Abbreviation for *Infrared Data Association*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### ISDN
Abbreviation for *Integrated Services Digital Network*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### ISP
Abbreviation for *internet service provider*; not *ISP provider*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### I/O
Abbreviation for *input/output*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### IPsec
Abbreviation for *Internet Protocol Security*.

### JPEG
Acronym for *Joint Photographic Experts Group* (pronounced "JAY-peg"). *JPEG* usually refers to the image compression standard that this group developed for color and grayscale images. It's not necessary to spell out *JPEG* on first occurrence.

### LAN
Acronym for *local area network*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### LCD
Abbreviation for *liquid crystal display*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### LCI
Abbreviation for *liquid contact indicator*. Spell out on first occurrence. In subsequent references, it's OK to say *LCI* or *the indicator*.

### LED
Don't use in user materials unless you have a specific reason (to distinguish from LCD, for example). Use *light* or *indicator light*.

### MIDI
Acronym for *Musical Instrument Digital Interface*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### MIME
Acronym for *Multipurpose Internet Mail Extension*, commonly used to distinguish an email format from plain text format. It's not necessary to spell out on first occurrence. Use as an adjective (*a MIME file*, *MIME format*).

### MIPS
Acronym for *million instructions per second*. Don't drop the *s* when you refer to a single unit: *1 MIPS*, not *1 MIP*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### MPEG
Acronym for *Moving Picture Experts Group*, a working group of the International Standards Organization (ISO). The acronym is pronounced "em-peg." It's not necessary to spell out on first occurrence.

### MP3
Short for *MPEG Audio Layer 3*, an audio compression technology. The plural is *MP3s*. Don't use *MP3* to refer to audio files in general; some files use AAC or other formats.

### PAL
Acronym for *Phase Alternating Line*, a European color video standard. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### PDF
Abbreviation for *Portable Document Format*. Not necessary to spell out on first occurrence. Use to refer to a PDF file.

### PIN
Acronym for *personal identification number*. When discussing iOS or iPadOS devices, use only to refer to the PIN used to unlock a SIM card. See also [code, passcode](word-choice-and-confusables.md#code-passcode).

### POP
Acronym for *point of presence* (access point to the internet) and *Post Office Protocol*. When used as an acronym for *Post Office Protocol*, *POP* must modify a noun (as in *POP server* or *POP ID*). For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### PRAM
Acronym for *parameter random-access memory*. Pronounced "PEA-ram." For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### RAID
Acronym for *Redundant Array of Independent Disks*, a storage method in which data is distributed among two or more hard disk drives to improve performance and reliability. Storage methods are called *levels*: *RAID level 0*, *RAID level 1*, *RAID level 0+1*, and so on. OK to shorten to *RAID 0*, *RAID 1*, *RAID 0+1*, and so on. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### RAM
Acronym for *random-access memory*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### RAW
A format for image files. Use all caps even though *RAW* is not an acronym. Don't use *RAW* alone; use *RAW file*, *RAW image*, *RAW setting*, and so on.

### RFI
Abbreviation for *radio-frequency interference*. Note hyphenation of the spelled-out version. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### ROM
Acronym for *read-only memory*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### RSS
Abbreviation for *Really Simple Syndication*. A format for displaying the latest changes to websites and blogs. Users access these RSS feeds with an RSS reader. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### RTF
Abbreviation for *Rich Text Format*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SAN
Acronym for *storage area network*. Precede with *a*, not *an*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SD
Abbreviation for *standard definition* (n.) and *standard-definition* (adj.). For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SDH
Short for *subtitles for the deaf and hard of hearing*. Define on first mention.

> Subtitles for the deaf and hard of hearing (SDH) differ from closed captions in several ways.

Use *SDH* when referring to the technology.

> You'll find SDH on more media types than closed captioning.

Use *SDH subtitles* when you're referring to the titles themselves.

### SDK
Abbreviation for *software development kit*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SDR (n., adj.)
Abbreviation for *standard dynamic range* (n.) and *standard-dynamic-range* (adj.). A legacy video or still-image format with limited levels of brightness per color component.

### SDRAM
Abbreviation for *synchronous dynamic random-access memory*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SIM
Acronym for *Subscriber Identity Module*, a smart card that holds subscriber information and settings. Precede with *a*, not *an*. OK to use *SIM* or *SIM card*. SIM formats include *micro-SIM* and *nano-SIM*. Related terms include *Apple SIM*, *embedded Apple SIM*, *Dual SIM*, and *eSIM*.

### SIMM
Acronym for *single inline memory module*. No hyphen in the spelled-out version. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SMTP
Abbreviation for *Simple Mail Transfer Protocol*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SO-DIMM
Acronym for *small outline dual inline memory module*. Note hyphenation of the acronym. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### S/PDIF
Acronym for *Sony/Philips Digital Interface Format*. Don't use *S/P-DIF*. The acronym is pronounced "spid-iff," so it's preceded by *a*, not *an*. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### SSD
Abbreviation for *solid-state drive*. Precede with *an*, not *a*. It's OK to use *SSD* alone or in terms such as *SSD storage*; don't use *SSD drive*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### TCP/IP
Abbreviation for *Transmission Control Protocol/Internet Protocol*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### UDF
Abbreviation for *Universal Disk Format*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### UFS
Abbreviation for *UNIX File System*, a file format available in Disk Utility that's used primarily by UNIX and UNIX-based operating systems. Not necessary to spell out on first occurrence.

### UI
Abbreviation for *user interface*. OK to use in developer materials. In user materials, use *interface*.

### UK
No periods. OK to abbreviate or to spell out *United Kingdom* as a noun. Use the abbreviation for the adjective form.

### UNIX
All caps; there's no spelled-out version.

### URL
Abbreviation for *Uniform Resource Locator*, which is another term for an internet address. *URL* is pronounced "you-are-ell" and should be preceded by *a*, not *an*. In most user materials, use *internet address* or *web address*, not *URL*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms). See also *internet addresses*.

### U.S.
Use periods except when the abbreviation appears close to other country or region name abbreviations that don't use periods. Use the abbreviation as an adjective only; as a noun, spell out *United States* (except in trademark notices). To include the country name in a U.S.-based Apple address, use *USA* (no periods). See also [America, American](#america-american).

### USB
Abbreviation for *Universal Serial Bus*. Avoid as a noun. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### USB connector types
There are several types of USB connectors (and corresponding ports):

- *USB Type-A:* On first mention, describe what the connector looks like (*rectangular*). OK to shorten to *USB-A connector* (or *USB-A port*).
- *USB Type-B:* On first mention describe what the connector looks like (*square*). OK to shorten to *USB-B connector* (or *USB-B port*).
- *USB Type-C:* A tiny USB connector that supports USB 3.1 and USB power delivery. OK to shorten to *USB-C connector* (or *USB-C port*).

### VPN
Abbreviation for *virtual private network* or *virtual private networking*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### VRAM
Acronym for *video random-access memory*. Pronounced "VEE-ram." For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### WAN
Acronym for *wide area network*. Note no hyphen in the spelled-out version. For guidelines about spelling out acronyms, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### WWDC
Abbreviation for *Worldwide Developers Conference*. For guidelines about spelling out abbreviations, see [abbreviations and acronyms](#abbreviations-and-acronyms).

### WWW
Don't use as an abbreviation for *World Wide Web*. Use *web* instead.

### file types
Abbreviations should be in all caps; filename extensions should be in lowercase. In most cases, you don't need to spell out on first occurrence. Use to refer to a specific kind of file, such as a JPEG file or a PDF file. Don't use *file format* (a file's structure and method of storing data) when you mean *file type*.

> Correct: PNG is a file type popular for web images.
> Incorrect: PNG is a file format popular for web images.

When possible, use just *file*.

> The photo is exported as a JPEG file.
> For better playback performance, Final Cut Pro transcodes all MP3 audio files to MOV audio files.

The following table shows the abbreviations and extensions for some common file types:

| Abbreviation | Extension |
|---|---|
| AIFF | .aif |
| CAF | .caf |
| DMG | .dmg |
| GIF | .gif |
| JPEG | .jpg |
| MP3 | .mp3 |
| PDF | .pdf |
| RTF | .rtf |
| TIFF | .tif |
| WAV, WAVE | .wav |

See also *file format*; *filename extensions*.

### America, American
Refers to both North and South America. Don't use when you mean *United States*. See also [U.S.](#us).
