I was looking at some code, saw a variable x, and said to myself, "Ah that variable is a monad." Then I realized "Monad" is the name of a type class. So maybe x should be called "an instance of a Monad." I think the word "instance" in this case is OO-like; but in Haskell "instance" refers to a type that is an instance of a type class. [...]
In general, it helps to know that the current "de facto" Haskell standard actually accepts classes and instances built on top of many types: class SomeClass a b c where someF :: a -> b -> c anotherF :: b -> c -> a instance SomeClass T1 T2 T3 where someF = ... anotherF = ... This way it becomes clear that saying that some type "is of" or "instantiate" some class isn't apropriate. Best, Maurício