Не вижу разницы, чесна

"a callback is a reference to a piece of executable code that is passed as an argument to other code. This allows a lower-level software layer to call a subroutine (or function) defined in a higher-level layer." - Wiki

"A delegate is a form of type-safe function pointer used by the Common Language Infrastructure (CLI). Delegates specify a method to call and optionally an object to call the method on. Delegates are used, among other things, to implement callbacks and event listeners. A delegate object encapsulates a reference to a method. The delegate object can then be passed to code which can call the referenced method, without having to know at compile time which method will be invoked." - Wiki