[orlandu63]

A monad is an abstraction for composing functions that return values with a context by defining how to compose that context. That's it.

[silentbicycle]

With the recognition that those functions have a common protocol / interface, and consequently have more in common that is usually noticed.

Monads aren't a new thing, rather they're giving a name to a concept that has been hiding in plain sight. Trying to look at them directly is confusing at first, like suddenly being able to explicitly manipulate continuations.