Emulation is the imitation of an object as another object. For example, a PlayStation emulator makes PlayStation game CDs recognize a PC as the machine where they are intended to run. Another example, a man puts on fake breasts, wear woman clothing and soften his voice to emulate a woman. So, basically an emulation has a purpose to make its environment recognize an object as another object. This is why emulator needs to be complete. If, for example, the man emulating a woman fails to emulate a woman completely like urinating while standing, he will be found out not to be a woman. About emulator, you usually says: "I want to make this stuff be recognized as that stuff so that another thing that I have in mind will continue to interact with the emulated stuff in the way it interacts with the real stuff".