Like if you have an Windows PC emulator, or the iOS one, you can run Windows or iOS appliactions on your Mac computer, especially good for app developers.
This in turn helps people to run different apllications exclusively for various OS on a single platform. It typically helps one OS to behave as another for as much amount of time as we want and then switch back to our original OS. Emulator is the software that helps us to run multiple OS on a single hardware.
