TL;DR: Abbreviations FTW by Stan Carey #repost

The following is a repost from here.

Abbreviations are an important feature of English, and they take various forms. They may be shortened titles (Ms, Mx, Dr, Capt.); clippings of longer words (influenza flu, disrespect dis(s), family fam); initials of foreign phrases, which themselves may be unfamiliar (e.g. ‘exempli gratia’, amante meridiem’ – see the Word story at each entry); and acronyms and initialisms.

Acronyms are spoken as one word, like AWOL and WASP, while initialisms are spoken as distinct letters, like rpm and VIP. This difference is not widely known, though, so acronym can be applied broadly to both types, and I do so here. In formal use, acronyms usually appear in all capital letters. Some publishers put them in title case (Unesco, Nasa), but this is relatively uncommon, and is resisted in some quarters. Laser, sonar, and scuba were fully lowercase almost from the start, and people may be surprised to learn they’re acronyms at all.

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