This is called a callback function, or a dynamic event handler. There’s something about it in the AS tricks section. And to answer your question, onRollOver is the name of the function.
OK, now concerning Lost code: Are you applying this to every button? I don’t understand. And secondly, you redefine the functions on EnterFrame, and each button will redefine its own function on EnterFrame, which is not a very good idea. Or maybe I didn’t understand you code.