Let me explain it more easy .
Server emulator (privat server) is a term that is used to refer to an internet server that mimics the behavior of another server that is usually more well known. This is implemented through cloning or reverse engineering of the original server. Other synonyms include server reimplementation, server engine recreation, or server-side emulation. The term is widely used to describe reimplementation of MMORPG game servers, typically unauthorized clones of proprietary commercial software by a third party. Technically, a server emulator does not emulate by the traditional definition, which would permit software from one hardware platform to run on a different one , it is more similar to a terminal emulator.Like with other game rates/armors/monsters/weopons & so on.