$\TeX$ is a typesetting system written by Donald E. Knuth, who says in the Preface to his book on TeX (see books about TeX) that it is “intended for the creation of beautiful books - and especially for books that contain a lot of mathematics”.

TeX is a macro processor, and offers its users a powerful programming capability. For this reason, TeX on its own is a pretty difficult beast to deal with, so Knuth provided a package of macros for use with TeX called Plain TeX; Plain TeX is effectively the minimum set of macros one can usefully employ with TeX, together with some demonstration versions of higher-level commands (the latter are better regarded as models than used as-is). When people say they're “programming in TeX”, they usually mean they're programming in Plain TeX.

$\LaTeX$ is a $\TeX$ macro package, originally written by Leslie Lamport, that provides a document processing system. LaTeX allows markup to describe the structure of a document, so that the user need not think about presentation. By using document classes and add-on packages, the same document can be produced in a variety of different layouts.

Lamport says that LaTeX “represents a balance between functionality and ease of use”. This shows itself as a continual conflict that leads to the need for such things as FAQs: LaTeX can meet most user requirements, but finding out how is often tricky.

<latex> $$\left[ {\bf X} + {\rm a} \ \geq\ \underline{\hat a} \sum_i^N \lim_{x \rightarrow k} \delta C \right]$$ </latex>

<latex> E=mc^2 </latex>

• latex.txt