As always, this is Grammar Girl, striving to be your friendly guide in the writing world. Other publications don’t put periods after each letter, arguing that the copy looks cleaner without them, and that because they are made up of all capital letters, the fact that they are abbreviations is implied.

Some publications put periods after each letter, arguing that because each letter is essentially an abbreviation for a word, periods are necessary. Abbreviations are any shortened form of a word.įinally, there’s no strict rule about putting periods after each letter in an acronym or initialism.

Examples include NASA, NIMBY (not in my backyard), and hazmat* (hazardous materials).

Acronyms are made from the first letter (or letters) of a string of words but are pronounced as if they were words themselves.

Examples include FBI, CIA, FYI (for your information), and PR (public relations).

Initialisms are made from the first letter (or letters) of a string of words, but can’t be pronounced as words themselves.

NASA, on the other hand, is an acronym because even though it is also made up of the first letters of the department name (National Aeronautics and Space Administration), it is pronounced as a word, NASA, and not by spelling out the letters N, A, S, A. FBI and CIA are examples of initialisms because they’re made up of the first letters of Federal Bureau of Investigation and Central Intelligence Agency, respectively, but they can’t be pronounced as words. They are often confused with acronyms because they are made up of letters, so they look similar, but they can’t be pronounced as words. Initialisms are another type of abbreviation. All acronyms are abbreviations, but not all abbreviations are acronyms. This makes them a subset of abbreviations. for October but acronyms are special kinds of abbreviations, such as ROFL (rolling on the floor laughing) and OPEC (Organization of Petroleum Exporting Countries), that can be pronounced as words. Any shortened form of a word is an abbreviation, for example, etc.

2 letter abbreviations for words