An emulator is one of the three period 4 oscillators that produce sparks similar to those produced by a lightweight spaceship, middleweight spaceship, or heavyweight spaceship. They are the lightweight emulator, middleweight emulator, and heavyweight emulator respectively. It is possible to construct larger emulators, but they require stabilizing objects to suppress their non-sparks and so are of little use (except for the overweight T-nosed p4). The three standard emulators were discovered by Robert Wainwright in June 1980. All of the p4 oscillators can eat gliders with their sparks.
"Emulator" has occasionally been used to refer to higher-period oscillators that produce sparks similar to other spaceships, but "volcano" is more commonly used specifically for period 5, or the generic "sparker" for other periods.