monad

What is it? Why is it so leet? Why do I need to use it for IO?

>>1
A monad is something you can connect in a sequence so that the choice of a step can depend on the results of previous steps. In other words, it's the most natural way to exress sequences of actions.

Here's an explanation by Tony Morris where he shows that even programmers in the less practical languages like C# and Java use monads all the time:
http://dl.dropboxusercontent.com/u/7810909/docs/what-does-monad-mean/what-does-monad-mean/chunk-html/index.html