LaTeX is a front end for the TeX text formatting system. Easier to use than TeX. LaTeX is essentially a set of TeX macros which provide convenient, predefined document formats for users. It also allows to compile LaTeX files directly to PDF format.

If you are installing tetex, so that you can use the TeX text formatting system, consider to install tetex-latex. If you are not an expert at TeX, you should also install the tetex-doc package, which contains documentation for TeX.