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. Examples include:
- 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 spell out a term
In general, when an abbreviation is likely to be unfamiliar to the audience, spell out the first mention of the term and immediately follow with the abbreviation, in parentheses. For all subsequent mentions of the abbreviation, use the abbreviation by itself.
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 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:
- File formats such as PDF or XML
- Units of measurement such as MB or GB
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.
Use the most common form of a word. If the full spelled-out word is common and easily understandable, use that rather than abbreviating. For example, write approximately instead of approx.
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).