Covariant: MyClass<out T>

The ordering of the generic types follows the ordering of the generic type parameters. Generic<T> ≥ Generic<S> for T ≥ S.

A generic type parameter marked with the out keyword can only appear in output positions such as read-only properties and return values.

Contravariant: MyClass<in T>

The ordering of the generic types is reversed from the ordering of the generic type parameters. Generic<T> ≥ Generic<S> for T ≤ S.

A generic type parameter marked with the in keyword can only appear in input positions such as write-only properties and method parameters. Not including ref and out parameters.

Invariant: MyClass<T> 

A generic type parameter is invariant if neither of the above apply.