That is the meaning of the acronym, MOO, but even this has an embedded acronym, MUD. The most appropriate current meaning for MUD is "Multi-User Domain."

A more functional definition is that MOOs and MUDs are text-based virtual reality environments that foster synchronous communication between persons and allow for creative building of virtual spaces. Many implementations of MOOs today incorporate web-based features so that the characteristic that a MOO is purely text-based is no longer totally accurate.