LATEX is a document preparation system for the TeX typesetting program.
It offers programmable desktop publishing features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout, bibliographies, and much more. LaTeX was originally written in 1984 by Leslie Lamport and has become the dominant method for using TeX—few people write in plain TeX anymore. The current version is LaTeX2ε.
Taken from Wikipedia - http://en.wikipedia.org/wiki/LaTeX.
See the G-Bar's dedicated LaTeX site.
Which tools can I use to edit LaTeX
We offer various editors for LaTeX which can be found in Downloads page of Latex support site.