Wiki versus Forum

I am having a difficult time trying to figure out what the difference is between a Wiki and the Forums, and how people would use them differently.

Because I have no understanding of the concept of a Wiki, I've been having our team use the Forums section as a way to record important workflow procedures. I'm guessing there's a way users do that with a Wiki, but I just don't understand the pro's and con's of how to use it.

Can anyone help me understand the concept of a "Wiki" a little better? Thanks so much in advance.