LaTeX is a comprehensive set of markup commands used with the powerful typesetting program TeX (developed by Donald E. Knuth) for the preparation of a wide variety of documents. Researchers, educators, and students in universities, as well as scientists in industry, use LaTeX to produce professionally formatted papers, proposals, and books. LaTeX (developed by Leslie Lamport) is an open source software system, available for download free of charge under LPPL.
LaTeX is not a word processor! Instead, LaTeX encourages authors not to worry too much about the appearance of their documents, but instead concentrate on getting the right content. LaTeX2e is now the standard version of LaTeX.