Grammar Girl here, today's topic is the difference between abbreviations, acronyms and initialisms.

Unfortunately, you can't call any abbreviation made up of a phrase's first letters and acronym,

sometimes their initialisms.

But let's back up.

Any shortened form of a word is an abbreviation.

For example, ETC, for etc., and OCT for October.

But acronyms are special kinds of abbreviations that can be pronounced as words, such as NASA for National Aeronautics and Space Administration,

and OPEC for Organization of the Petroleum Exporting Countries.

This makes acronyms a subset of abbreviations.

All acronyms are abbreviations, but not all abbreviations are acronyms.

Initialisms are another type of abbreviation.

They're often confused with acronyms, because they're made up of letters, so they look similar.

But they can't be pronounced as words.

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 aren't usually pronounced as words.

Insiders sometimes call the FBI Fibby and the CIA SEA, but most of the worlds has FBI and CIA, so they're initialisms.

So remember, initialisms are made up of the first letter or letters of a string of words, but can't be pronounced as words themselves.

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

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 NASA and NIMBY for not in my backyard.

Abbreviations are any shortened form of a word.

Sometimes acronyms like SCUBA become so common that they're accepted as words in their own right.

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