MOO stands for ``MUD, Object Oriented.'' MUD, in turn, has been said to stand for many different things, but I tend to think of it as ``Multi-User Dungeon'' in the spirit of those ancient precursors to MUDs, Adventure and Zork. MOO, the programming language, is a relatively small and simple object-oriented language designed to be easy to learn for most non-programmers; most complex systems still require some significant programming ability to accomplish.
notify(player, "Hello, world!");