Wildcards are a way to provide partial support for propert generics, in which—if B inherits from A—List<B> also inherits from List<A>. In both Java and C#, this is not the case, which makes passing generic parameters all the more difficult.

The where keyword in C# corresponds to the extends keyword in Java. It indicates that the actual generic parameter must conform to the given base type (which can be a class or an interface). In your example, the implementation of the generic class may call any features defined in MYBASETYPE on MYTYPE.