Property based testing means automatically generating data and testing whether the code aligns with the property or not

A good generator has few to none discarded values in the generator space (where the precondition fails on a generated value).

A QuickCheck Property is a combination of a precondition, a postcondition and a generator.

Testable is for types that can be translated into a property. For example, Bool.

Arbitrary is for types you can randomly draw elements from.