I have been using this more frequently now in Java but I don't know what it is called. Essentially there is a function which takes a type as a param and within the function there are overridden functions/methods that can be used. These functions can be executed within functions that are exposed by the main class. For example:

public class Whatisthis {

    private OtherLibsomeCallback theCallback;

    public void dothatthang{

        //What do you call this kind of code structure?
        someCallback(window, theCallback = new OtherLibsomeCallback() {

            @Override
            public void invoke(long a, double b) {
                // TODO Auto-generated method stub
                globalVar = a + b;
            }
        });
    } 
}