Rosetta is an emulator (or, I suppose, a series of emulators), i.e. a piece of software that makes a computer pretend to be another kind of computer. This is also a bit of lower level software that makes a (x86_64) computer pretend to be a different kind of computer (aarch64), in this case, by AoT and JIT translation, though that's an implementation detail. What distinction are you trying to make?