Acronym

A word formed from the initial letters of a phrase — and the specific, commonly blurred distinction between an acronym and an initialism.

What it is

An acronym is a word formed from the initial letters (or parts) of a longer phrase — NASA, from National Aeronautics and Space Administration; RADAR, from RAdio Detection And Ranging.

Acronym vs. initialism

Strictly, an acronym is pronounced as a single word (NASA is said "NASS-ah," not "N-A-S-A"). When the letters are instead pronounced individually — FBI, HTML, URL — the more precise term is initialism, not acronym. In everyday usage "acronym" is commonly used to cover both, and this glossary follows that common usage elsewhere, but the distinction is real and worth knowing if you're writing about writing.

Why acronyms complicate case conversion

Inside a programming identifier, an acronym is exactly what breaks a naive tokenizer. A name like HTMLParser or parseXMLHttpRequest contains a run of capital letters that represents one unit (HTML, XML), not several one-letter words. Splitting on every capital letter — the simplest possible approach — shreds the acronym into single characters. A tokenizer that specifically detects ALLCAPS runs is what keeps HTMLParser converting to html_parser instead of h_t_m_l_parser.

How title-case style guides treat acronyms

In prose titles, acronyms are generally left in their conventional all-caps form regardless of what the title-case rule would otherwise do to that word — "NASA Launches New Satellite," not "Nasa Launches New Satellite." Every style guide on this site preserves recognized acronyms as-is during conversion rather than reshaping them, the same way it preserves proper nouns.

Where this shows up

Both the programming case converters and the title case converter use the same underlying acronym-detection logic, so an acronym behaves consistently whether it's sitting inside a variable name or a headline.

Source

Merriam-Webster — "acronym", including its usage note on the acronym/initialism distinction.

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