What the Heck's a Code Monkey?

I was cruising around ThinkGeek when I came across these shirts:

This one says "Code Monkey,"

And this one says "Killer Coding Ninja Monkeys Do Exist."

My question is, like the title says, WHAT THE **** IS A CODE MONKEY?!?!? Also, what's the difference between a Code Monkey and a Killer Coding Ninja Monkey? Any info you could provide would be much appreciated.

On another note, now that I've discovered that I can use Blogger Beta Spell-Check without fear of my posts being un-formatted, I've gone back and Spell-Checked all the chapters of More Than a Job. I also did a bit of minor editing while I was at it, so feel free to check that out. *nudge* *nudge* *wink* *wink*