TeX (tech) is a typesetting system and LaTeX (lah-tech) is a markup language for TeX typesetting.
TeX, LaTeX, and other related programs are used primarily for complex typesetting tasks in fields such as mathematics, science, and engineering although they can be used for just about anything that we normally use desktop publishing for. TeX, the typesetting system, was designed in the late 1970s by Donald Knuth. LaTeX, a document markup language used to prepare documents for the TeX system, was developed in the 1980s and is the primary (although not only) method of using TeX. TeX and related programs are freely available.
The level of precision in typesetting that can be achieved with TeX, especially for complex mathematical and scientific equations and formulas, is superior to the formatting available in most word processing and WYSIWYG desktop publishing software programs.
One way to think of TeX and LaTeX is to think of how some people produce Web pages using plain text editors with hand coding instead of a WYSIWYG editor. You would type the text in a plain text editor then wrap the text in various codes (HTML -- hypertext markup language) that tells the Web browser how to display the text (bold type, sans serif fonts, etc.) and the pages (columns, tables, etc.). Also see: Tagged Text
For more details on the history of TeX and LaTeX and how to use it:
- What are TeX, LaTeX and friends? CTAN - The Comprehensive TeX Archive Network
- Starting Out With TeX, LaTeX and friends CTAN
- Just What is TeX? TUG - TeX Users Group
- TeX FAQ The UK TeX Archive
- Desktop Publishing on Linux with TeX David S. Jackson
"The only free DTP program that equals InDesign is TeX. In fact InDesign uses the TeX paragraph at a time justification. I typeset books for money using the pdftex variant." —wexfordpress