What does "theology" really mean?

Okay, so I'm writing this paper on Voltaire's "A Plea for Tolerance and Reason" and i have to answer the question "Why did Voltaire ridicule Christian theology? And I can't answer it because I don't know what theology means. I looked it up but in the dictionary it just babbles on and I can't get the real idea of what it is.. so in lamens terms, can anybody explain it to me? If you know Voltaire's works and could help me out with that, it would help too (hehe) thanks!