TeX is a free, cross-plaform typesetting system that allows the creation of high-quality documents, mainly scientific and technical publications.
Documents (usually .tex files) are typeset in a mixed programming/markup language which is then read by the TeX program to emit the output (.pdf, .dvi, among others).
Currently, TeX is mainly used in the academia mostly because of its remarkable rendering and high-quality output of complex mathematical expressions and typographic capabilities.
There are a few macro (command) packages available which extend TeX's abilities and simplify writing. One of the most well known macro packages is LaTeX, which provides commands to structure documents (create sections, chapters, cross-references, etc.) and other things, essentially giving the user a high-level language to harness the power of TeX.
|.ltx - LaTeX Document (Document Files)
.ltx files are used by the TeX typesetting system, most commonly with the LaTeX macro package. There files usually contain pre-coded commands to be included... [More Information]
|.tex - LaTeX Source Document File (Text Files)
.tex files are used by the TeX typesetting system, most commonly with the LaTeX macro package. These files contain instructions describing the precise... [More Information]