TeX is a typesetting system that incorporates a macro processor. A TeX source document specifies or incorporates a number of macro definitions that instruct the TeX engine how to typeset the document. The TeX engine also uses font metrics generated by , or by any of several other mechanisms that incorporate fonts from other sources into an environment suitable for TeX.

TeX has been, and continues, a basis and an inspiration for several other programs, including and .

The distribution includes the source of Knuth’s TeX book; this source is there to read, as an example of writing TeX — it should not be processed without Knuth’s direct permission.

The author is Donald E. Knuth. The package is Copyright © 1982 D. E. Knuth.