Fold Equity (Request for Definition and Examples)

[BiiiiigChips]

I see the term Fold Equity (FE) thrown around alot on the boards. I've read a few poker books but I don't think I've ever seen the topic addressed in any of them, at least not at length. So for the posters of 2+2 what is the meaning of the term Fold Equity and what are some examples of some situations where your Fold Equity is high, low, or not a factor?