Keyword

A keyword, also known as reserved words, is a word that cannot be used as an identifier, such as the name of a variable, function, or label – it is "reserved from use".

List of Reserved Words in Lua
Names starting with and underscore, but followed by uppercase letters (such as _VERSION) are reserved for internal global variables used by Lua.
 * and
 * break
 * do
 * else
 * elseif
 * end
 * false
 * for
 * function
 * if
 * in
 * local
 * nil
 * not
 * or
 * repeat
 * return
 * then
 * true
 * until
 * while