What do you call a collection of types that obey certain restrictions?

Question

For function

f :: Vector a => a -> b 

we will call a type (or type variable) and Vector constraint. But what do we call the collection of all types satisfying Vector a => a ? I unofficially called it a "set of vector spaces", and I call any type of member "vector space". Are there more precise set-theoretic names that I should use? In particular, are the words "set" and "space" used correctly?