The term variance describes how subtyping between higher kinded types is related to subtyping relations of their type arguments.
Higher Kinded Types
A higher kinded type composes type arguments to a new type. I use square bracket notation to define a higher kinded type:
C[T] // The higher kinded type `C` composes type argument `T` to a new type `C[T]`.
The same works with multiple type arguments: