There are many different definitions of “what is an emulator”? or “what is the function of an emulator”?.
I will list a few of the definitions,and hope they may answer your question.
1 – An emulator provides game enthusiasts with the opportunity to play games from other gaming platforms,an emulator also allows gamers to play games from older systems,or that may no longer exist.
2 – Emulation refers to the ability of a computer program or electronic device to imitate another program or device.
3 – A console emulator is a software program that duplicates a computer or gaming console to emulate a video game,so that it acts or imitates like the original. For an example if you want to play a game from the Nintendo or Sega gaming platform,you must download an emulator for that said game.Each game has an individual emulator.
4 – Gamers can use emulators to modify existing games – ie translate games into different languages.
5 – An emulator,provides conversion software that will enable a game to run on a computer or another system or platform for which it was not originally designed for.
6 – An emulator is a software program that can imitate the original hardware environment of a gaming console.This means that an emulator will “emulate” a gaming console’s hardware capabilities and so game software that was developed for specific hardware can be run on your computer via the emulator
You can view further information on emulators at Wikipedia.