LaTeX is a document markup language and document preparation system 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.

Install an appropriate package:

TexLive2011 sfs packaged by Emil

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

Lyx

WikiPedia:LaTeX - language

WikiPedia:TeX - system