Abbreviations include acronyms, initialisms, shortened words, and contractions.

In most contexts, the technical distinction between acronyms and initialisms isn't relevant; it's fine to use the word acronym to refer to both.

  • An acronym is formed from the first letters of words in a phrase, but is pronounced as if it were a word itself:
    • NATO for North Atlantic Treaty Organization
    • scuba for self-contained underwater breathing apparatus
  • An initialism is also formed from the first letters of words in a phrase, but each letter is pronounced separately:
    • CIA for Central Intelligence Agency
    • FYI for For Your Information
    • PR for Public Relations
  • A shortened word is just part of a word or phrase, sometimes with a period at the end:
    • Dr. for doctor
    • etc. for et cetera
    • min for minutes
    • CA for California
  • Contractions are discussed in a separate page of this style guide.

There's some overlap among those categories. In particular, some abbreviations can be either acronyms or initialisms, depending on the speaker's preference—examples include FAQ and SQL. In some cases, the pronunciation determines whether to use a or an.

Long and short versions of a word

Some words have a long version and a short version—for example:

  • application and app
  • demonstration and demo
  • synchronize and sync

The short versions of the words are not abbreviations, and if you use them, you don't need to put a period after them.

If you're not sure whether a word is an abbreviation or just a short version of a longer word, look in our list of resources. If that doesn't settle the issue, use the speaking test: if you speak the short version as a word (This is a demo version of the product), you can usually treat it as a word and not an abbreviation.

When to use abbreviations

Abbreviations are intended to save the writer and the reader time. If the reader has to think about an abbreviation, it can slow down their reading comprehension.

General dos and don'ts

  • Use standard acronyms and initialisms that will save the reader time.
  • Spell out abbreviations on first reference. For more information, see When to spell out a term.
  • Avoid using abbreviations for terms that aren't related to the main topic of the document.
  • In the following examples, the main topic of the document is the internet of things, so low Earth orbit should not be abbreviated.

    Recommended: The internet of things (IoT) service can even be used for connecting to sensors in low Earth orbit.

    Not recommended:The IoT (internet of things) service can even be used for connecting to sensors in LEO (low Earth orbit).

  • Be wary of using specialized abbreviations that your readers might not understand. For more information about when to use such language, see Jargon.

When to spell out a term

In general, when an abbreviation is likely to be unfamiliar to the audience, spell it out upon first mention and include the abbreviation in parentheses immediately following. Italicize both the spelled-out term and its abbreviation.

Recommended: Border Gateway Protocol (BGP)

Not recommended: Border Gateway Protocol (BGP)

For all subsequent mentions of the abbreviation, use the abbreviation by itself. If you use an abbreviation only once, include it only if you think the abbreviation is as commonly used as the spelled-out term. Otherwise, don't include the abbreviation.

Capitalize the spelled-out version of the abbreviation only if the long form is a proper noun or is conventionally capitalized. That is, don't capitalize it only because the abbreviation includes capital letters.

If the first mention of a term occurs in a heading or title, you can use the abbreviation and then spell out the abbreviation in the first paragraph that follows the heading or title.

When deciding to spell out a term, consider your audience. If your document is going to be translated, spelling out a term can provide important context for both human and machine translation. It can also be helpful for readers who aren't as familiar with English. If the majority of your audience is likely to recognize and understand the term, then you don't need to spell it out. For example, if you're writing documentation for developers that references an API, you don't need to spell out application programming interface. However, if you're explaining the general concept of an API to someone with no programming experience, spelling out the abbreviation can be helpful.

In some cases, spelling out a term doesn't help the reader understand the term. For example, writing out portable document format doesn't help the reader understand what a PDF document is. In those cases, don't spell out the term.

The following abbreviations rarely need to be spelled out:

  • API
  • DVD
  • File formats such as PDF or XML
  • HTML
  • PC
  • RAM
  • REST
  • Units of measurement such as MB, MiB, GB, or GiB
  • URL
  • USB

Abbreviations not to use

Prefer English terms over Latin abbreviations. Don't use i.e. or e.g.; instead, use that is or for example, respectively. One exception: it's okay to use etc. in some circumstances.

Don't use internet slang abbreviations such as tl;dr, ymmv, RTFM, or others. Write out what you mean in a non-figurative way.

Use the most common form of a word. If the spelled-out word is common and easily understandable, use that rather than abbreviating. For example, write approximately instead of approx.

Spell out shortened words or common symbols that are substitutions for words.

Recommended: Updating the software made throughput 10 times faster.

Not recommended: Updating the software made throughput 10x faster.

Periods with abbreviations

Follow these guidelines:

  • Don't use periods with acronyms or initialisms.
  • Put a period at the end of a shortened word, except for date and time abbreviations.
  • If you write or say an abbreviation as a word (for example, app or sync), don't put a period after it.
  • Don't use a period with an abbreviation for the name of a country, US state, or the District of Columbia (DC).

Make abbreviations plural

In general, treat acronyms, initialisms, and other abbreviations as regular words when making them plural—for example, APIs, SKEs, and IDEs.

If the acronym, initialism, or abbreviation ends in s, sh, ch, or x, then add es—for example, OSes, DISHes, DCCHes, and BMXes.

Abbreviations as verbs

Don't use acronyms, initialisms, or shortened words as verbs.

Recommended: Use SSH to log in to your remote shell.

Not recommended: Then ssh into your remote shell.