Function Closures

I first heard about the term "function closures" when I was studying functional programming languages in college. I had used some first-class functions before then, but I didn't really have any of the terminology down. College helped with the terminology a bit, but the term "closure" didn't really get solidified in my head. The term has been passed around a bit, and I knew that it was some kind of reference to a function, but it just wasn't solid in my head. I'd read definitions, probably ones that weren't written very well, but I never really needed to know the term.

Well, I was reading through Eric Lippert's blog (warning: I've been told that his color scheme is annoying to some), and I read his article on closures. Since then, I've never had any trouble. I'd been using closures all this time, but didn't know how they differed from more simple function references. I'd summarize, but then I'd just be compounding the problem.