The Web Content Style Guide: An Essential Reference for Online Writers, Editors, and Managers

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abbreviations and acronyms

Acronyms are abbreviations that form words from the first letter or letters in a series of words. For example, DOS is an acronym (as well as an abbreviation), while CPU is an abbreviation only as it does not form a word.

Abbreviations that are formed by using the first initials of separate words should not have any periods after the letters:

WAN, US, UK, PDF

Make an acronym or abbreviation plural by adding an s (no apostrophe), for example

WANs, PDAs

The article (a or an) that an abbreviation or acronym takes depends on the way it is pronounced—an if it’s before a vowel sound, a before a consonant sound

an IBM computer

an FTP program (pronounced with a vowel sound)

a DOS command

a UN resolution (although UN starts ...