TeX , by Donald E. Knuth, is a computer type-setting system and markup language that heralded a revolution in the quality of the vast majority of published mathematics.

The ideal is to be able to describe important classes of documents in terms of their components, without mentioning actual fonts or point sizes or details of spacing; a single style-independent document can then be set in many different styles.
-- Donald Knuth, The TeXbook .

See Also

write TeX Tcl-style
a lightweight clone of (a subset of) LaTeX, aimed at producing formula rendering for web pages and the like. It does not depend on having TeX or its fonts available.
a text editor/IDE designed to make editing TeX documents easier. http://tcltexed.sourceforge.net/screenshot/screenshot2.gif


TeX is mostly used via LaTeX, which is built on top of it.