In computer science, a monad is a notation representing an intermediate value and its computational context. E.g., data necessary to continue the next steps of

In computer science, a monad is a notation representing an intermediate value and its computational context. E.g., data necessary to continue the next steps of a calculation, or some kind of marker of the value's source (IO monad.) It's an abstraction which rarely carries its own weight, but it's necessary to understand Haskell for what seem to amount to cultural reasons. Other strongly typed functional languages don't place nearly so much emphasis on it.