TLA /T-L-A/ n.
[Three-Letter Acronym] 1. Self-describing abbreviation for a species with which computing terminology is infested. 2. Any confusing acronym. Examples include MCA, FTP, SNA, CPU, MMU, SCCS, DMU, FPU, NNTP, TLA. People who like this looser usage argue that not all TLAs have three letters, just as not all four-letter words have four letters. One also hears of `ETLA' (Extended Three-Letter Acronym, pronounced /ee tee el ay/) being used to describe four-letter acronyms; the terms `SFLA' (Stupid Four-Letter Acronym), `LFLA' (Longer Four Letter Acronym), and VLFLA (Very Long Five Letter Acronym) have also been reported. See also YABA.
The self-effacing phrase "TDM TLA" (Too Damn Many...) is often used to bemoan the plethora of TLAs in use. In 1989, a random of the journalistic persuasion asked hacker Paul Boutin "What do you think will be the biggest problem in computing in the 90s?" Paul's straight-faced response: "There are only 17,000 three-letter acronyms." (To be exact, there are 26^3 = 17,576.) There is probably some karmic justice in the fact that Paul Boutin subsequently became a journalist.
But not, as yet, a Federal Agency designation "TLA" that I'm aware of.