LaTeX is a document markup language and document preparation system originally for the TeX typesetting program. The term LaTeX refers only to the language in which documents are written, not to the editor application used to write those documents.

It is most often used for medium-to-large technical or scientific documents but it can be used for almost any form of publishing.

Install an appropriate package:

TexLive2011 sfs packaged by Emil

Note: the LaTeX system libraries are often packaged with the editor.

Lyx

Textext - plugin for Inkscape

Latex homepage

WikiPedia:LaTeX - language

WikiPedia:TeX - system