A terminal emulator is the software application you use to bring the command prompt up. So a terminal emulator is operating system agnostic.
Granted there are some macOS only terms out there like iTerm2 and Apples own Terminal. Just as there are terminals that haven't (as far as I'm aware) been ported to macOS, like xterm. But there's plenty of cross platform terminal emulators too, in fact most are cross platform.