A function that take one type and gives you another type. So (in Java for example) you have a generic type such as List<T>. But that is not a really a type because you can't have a value of the generic type. It is actually a type constructor, you can give it another type (say String) and it will give you a type List<String> which can actually be instantiated to a value. So in the context of programming languages it is just a fancy word for a generic or parametric type.