Three-letter Acronym

A three-letter acronym, three-letter abbreviation, or TLA is an abbreviation, specifically an acronym, alphabetism, or initialism, consisting of three letters. These are usually the initial letters of the words of the phrase abbreviated, and are written in capital letters (upper case); three-letter abbreviations such as etc. and Mrs. are not three-letter acronyms.

Most three-letter abbreviations are initialisms: all the letters are pronounced as the names of letters, as in APA /ˌeɪpiːˈeɪ/AY-pee-AY. Very few fit the strict definition of acronym, which requires the abbreviation to be pronounced as a single word, as in DOS /ˈdɒs/DOSS. When TLA stands for three-letter abbreviation, then TLA has the self-referential feature that TLA is its own TLA (and is thus autological). When TLA stands for three-letter acronym, this feature does not apply (as it is an abbreviation but not an acronym).