three-letter abbreviation

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, but "TLA" itself is a TLA (an example of a self-referencing definition).