If you know people interested in programming language theory, you will have heard of the monad. Especially in Haskell, they are used extensively. When trying to find out what they are, exactly, the average programmer will have a distinct Matrix feeling, though: You can not be told what a Monad is! Lots and lots of websites try to explain what a monad is, so many that you must wonder what an exceptionally awesome concept this is that it can not be explained in simple, understandable terms, but is still so important that people will not simply give up on using it.
After watching a Google Tech Talk presentation recently, I was enlightened as to how monads can be explained to normal programmers.