Emulator is a computer program that enables a host system to act as a guest system. This process is also called Emulation. When it came to gaming consoles then we can say it’s an alternative of them. That is used to play the game ROMS on any device. But be sure to download the related emulator according to the device.
For example if you want to run GBA files on android devices then you must download GBA emulator that is available for android.
Here is collection of Emulators that are available for different platforms.