The MOO consists of a series of objects. The most important objects are the rooms, which are linked by exits.
Players are objects, too, and so are the furniture, things, notes, and other things.
The generic container is a generic thing, but it can also be can be opened or closed, and things can be put inside of it. The generic note can be written on and read by others. With several modifications, the generic thing and the generic note were combined into both a generic slide projector capable of projecting text to everyone in the room, and a robot capable of listening for words and responding with preset answers. Your new thing would then have all of the qualities of the thing you based it on. Much of the power of the virtual-reality effect of the MOO rests in the descriptions of the rooms and the nature of transitions through the exits.