It's all Geek to me?

[Steve]

Howdy,
I was reading a book on Lua today and ran across a term I've seen a
hundred times, and still have not quite gotten a grip on.
I'm hoping someone can explain what this quote means...

http://www.lua.org/pil/6.html
"(It also means that Lua contains the lambda calculus properly.) "

Lamda Calculus, according to wikipedia, is a formal system designed to
investigate function definition, function application, and recursion.

Ok so I know how to a define a function, I know how to determine if a
function is applicable to the situation at hand, and I know what
recursion is.

But what the heck does it mean to "contain the lambda calculus properly"?

Thoughts?