'this' global variable

[Nuckin]

I have programmed in many language including C/C++, Java, BASIC, PHP, Python, Bash... etc, but Lua is the only one (maybe its just the Blizzard interpretation of Lua) with a global variable 'this'.

In all original code I have written, I haven't used it once. But right now I'm working on updating an addon to be 100% compliant with 3.0.x's deprecation of this variable. Some of the 'this' calls I have hacked out using 'self' (which I have figured out).

So what I'm getting at is what is 'this'? Any light people could shed on this would be awesome, I have yet to find a formal definition anywhere on google or in any books I own.