What is a "First Class" type?

Question

What does it mean for a type T to be a "First Class" type?

Answer 1

Usually it means instances of T can be

• returned from functions
• passed into functions
• constructed at runtime

Eg functions in C are not first class types as they cannot be constructed at runtime, but they are in JavaScript.

Answer 2

I think a first-class type is about the same thing as a first-class object. It's basically the type which provides the properties of a first-class object.