1. /tekh/ n. An extremely powerful macro-based text formatter written by Donald E. Knuth, very popular in the computer-science community (it is good enough to have displaced Unix troff, the other favored formatter, even at many Unix installations). TeX fans insist on the correct (guttural) pronunciation, and the correct spelling (all caps, squished together, with the E depressed below the baseline; the mixed-case `TeX' is considered an acceptable kluge on ASCII-only devices). Fans like to proliferate names from the word `TeX' -- such as TeXnician (TeX user), TeXhacker (TeX programmer), TeXmaster (competent TeX programmer), TeXhax, and TeXnique. See also CrApTeX. Knuth began TeX because he had become annoyed at the declining quality of the typesetting in volumes I-III of his monumental "Art of Computer Programming" (see Knuth, also bible). In a manifestation of the typical hackish urge to solve the problem at hand once and for all, he began to design his own typesetting language. He thought he would finish it on his sabbatical in 1978; he was wrong by only about 8 years. The language was finally frozen around 1985, but volume IV of "The Art of Computer Programming" is not expected to appear until 2002. The impact and influence of TeX's design has been such that nobody minds this very much. Many grand hackish projects have started as a bit of toolsmithing on the way to something else; Knuth's diversion was simply on a grander scale than most. TeX has also been a noteworthy example of free, shared, but high-quality software. Knuth offers a monetary awards to anyone who found and reported bugs dating from before the 1989 code freeze; as the years wore on and the few remaining bugs were fixed (and new ones even harder to find), the bribe went up. Though well-written, TeX is so large (and so full of cutting edge technique) that it is said to have unearthed at least one bug in every Pascal system it has been compiled with. From Jargon Dictionary

2. A popular macro-based text formatter. The basis for other such formatters, including LaTeX and teTeX. From I-gloss

3. An extremely powerful macro-based text formatter written by Donald E. Knuth, very popular in the computer-science community (it is good enough to have displaced Unix troff, the other favored formatter, even at many Unix installations). From Linux Guide @FirstLinux

4. text formatting and typesetting From whatis