For any type `a`, `Maybe a` is a type. We say "Maybe" in the same sense we say "List" -- it's obviously a list of some type `a`, but if what we're saying doesn'

For any type `a`, `Maybe a` is a type. We say "Maybe" in the same sense we say "List" -- it's obviously a list of some type `a`, but if what we're saying doesn't depend on any particular choice of `a`, then by abuse of language, we don't bother saying it. On the other hand, `Just` and `Nothing` are constructors, or variants, for values of type `Maybe a`. You can think of them as almost like static factories (as in `Optional.empty()` and `Optional.of(val)` in Java), except that algebraic constructors are invertible: you can match on a value to determine whether it was constructed with `Just` or `Nothing`, and what the arguments to the constructor were.