LaTex is yet another editor for documents - well rather one of the very first ones from back then where graphical environments was not on everybody's desk.
From Tobias Oetikers fine introduction to LaTex:
"TEX is a computer program created by Donald E. Knuth . It is aimed at typesetting text and mathematical formulae. Knuth started writing the TEX typesetting engine in 1977 to explore the potential of the digital printing equipment that was beginning to infiltrate the publishing industry at that time, especially in the hope that he could reverse the trend of deteriorating typographical quality that he saw affecting his own books and articles. TEX as we use it today was released in 1982, with some slight enhancements added in 1989 to better support 8-bit characters and multiple languages. TEX is renowned for being extremely stable, for running on many different kinds of computers, and for being virtually bug free. The version number of TEX is converging to π and is now at 3.141592653.
TEX is pronounced “Tech,” with a “ch” as in the German word “Ach” or in the Scottish “Loch.” The “ch” originates from the Greek alphabet where X is the letter “ch” or “chi”. TEX is also the first syllable of the Greek word τεκνολογία (technology). In an ASCII environment, TEX becomes TeX.
LaTeX enables authors to typeset and print their work at the highest typographical quality, using a predefined, professional layout. LaTeX was originally written by Leslie Lamport. It uses the TEX formatter as its typesetting engine. These days LaTeX is maintained by Frank Mittelbach. LaTeX is pronounced “Lay-tech” or “Lah-tech.” If you refer to LATEX in an ASCII environment, you type LaTeX. LATEX 2ε is pronounced “Lay-tech two e” and typed LaTeX2e. "