Lua
Lua, according to its own website lua.org is a powerful, efficient, lightweight, embeddable scripting language. This makes Lua ideal for configuration and extensions of other programs, also because of its great interoperation with C. The basic Lua interpreter is less than 250kB in size.
Available versions
There are currently multiple versions available in the official repositories. The most recent version 5.3 is referenced as just lua while the other available versions are 5.2 lua52 and 5.1 lua51. As the official implementation is written in ANSI C it is available for many platforms and architectures.
LuaJIT
The repositories also offer the LuaJIT, a Just-in-time compiler as luajit which implements the language as version 5.1. This version is best suited for higher performance constrains.
Language overview
For a detailed description please refer to the Lua reference manual.