- TeX is a typesetting language. Instead of visually formatting your text, you enter your manuscript text intertwined with TeX commands in a plain text file. You then run TeX to produce formatted output, such as a PDF file. Thus, in contrast to standard word processors, your document is a separate file that does not pretend to be a representation of the final typeset output, and so can be easily edited and manipulated.
TeX itself is only one component of what many consider to be a complete TeX distribution. For example, there exist a number of macro packages (also known as TeX formats) such as LaTeX and Plain TeX that simplify TeX applications at the cost of flexibility. Internally, TeX makes use of Metafont to define the shapes of glyphs and the relations between them.
TeX Live is a complete and comprehensive TeX distribution available in the official repositories that includes all the major TeX-related programs, macro packages, and fonts. The older (discontinued) teTeX distribution is available in the AUR.