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An acronym is an abbreviation made from the initial (first) letters of a group of words (and pronounced as a word), like this:

N[orth] A[tlantic] T[reaty] O[rganization] NATO

Sometimes only the more important first letters are included:

O[rganization] [of the] P[etroleum] E[xporting] C[ountries] OPEC

And sometimes the first two or three letters of a word may be used:

ra[dar] d[etection] a[nd] r[anging] radar

Here are some more examples:

acronym full form
Aids acquired immune deficiency syndrome
laser light amplification by stimulated emission of radiation
NASA National Aeronautics and Space Administration
PIN personal identification number
quango quasi-autonomous non-governmental organization
scuba self-contained underwater breathing apparatus
sim subscriber identification module
TEFL Teaching English as a Foreign Language
UNESCO United Nations Educational, Scientific and Cultural Organization
vat value added tax


Generally speaking, acronyms are not punctuated at all. There is no need to use full stops/periods.

If the acronym's full form uses capital letters, then the acronym usually uses capitals too (National Aeronautics and Space Administration → NASA). Some acronyms may be written with the first letter uppercase and the rest lowercase (acquired immune deficiency syndrome → Aids). Many acronyms have developed into words in their own right and may use entirely lowercase (subscriber identification module [card] → sim [card]).

Whether to use capitals or not is often a matter of style. If in doubt over the name of an organization (for example NASA or Nasa?) you can usually follow the organization's preferred style found on its website. For more general acronyms, a good dictionary will usually show the standard form.

Note that some acronyms can also be initialisms. For example, the abbreviation for Value Added Tax (or value added tax) is:


All acronyms can be pronounced as words, and many of them have indeed become dictionary words in their own right.

write and say: Aids - laser - NASA - PIN - quango - scuba - sim - TEFL - UNESCO - vat

acronym (noun): An abbreviation formed from the initial letters of other words and pronounced as a word (e.g. ASCII, NASA) - Oxford Dictionaries