Re: [Haskell-beginners] explaining effects

What is the exact defintion of "effect".

let's try: effect: A change which is a consequence of an action (in this case, function call) side effect: change of environment state which is a consequence of an action (function call) pure function: calling this function does not affect environment state function returns a value, that's all I am not sure if function running inside e.g. state monad and modifying this monad's state is pure, i.e. if state monad is environment