The LuaTeX engine provides access to OpenType fonts in a similar way
to XeTeX, and most uses of the fontspec package work equally well
with either engine.
LuaTeX also extends TeX in other ways, notably by embedding the Lua scripting language. This may be used for programming in a style more familiar to people used to ‘mainstream’ programming languages. It also offers the possibility to access inner workings of the TeX system and modify the behaviour by substituting new code written in Lua.
Lua programming is not covered by this course but a simple example to calculate 2π is shown here.
%!TEX lualatex
\documentclass{article}
\begin{document}
$ 2\pi \approx \directlua{ tex.print(2 * math.pi) } $
\end{document}