The TLA (three-letter abbreviation or acronym) is the most popular type of abbreviation in computing and telecom terminology and Internet slang, and is also common in political jargon. Some of these, such as "DOS", are strict acronyms, while others, like "TLA" itself, are initialisms; this distinction is not universally accepted (see the latter article for a discussion), but leads to the use of abbreviation as opposed to acronym in expanding the term.
In the MS-DOS operating system for personal computers, because only three-letter file extensions (usually denoting the file type) were allowed, many longer abbreviations were shortened to three letters (for example JPEG to JPG, HTML to HTM). Many abbreviations, some of them TLAs, come from the shortened names of Usenet groups. For example pra for pl.rec.anime.
