Emulation is basically the emulating or copying of something. Emulation is usually known of on the internet for emulating video games like nintendo, gameboy, sega genesis, and even some arcade games on the PC. These types of systems can be used on your computer with something called an Emulator. The Emulator is the name for the running system, like nintendo, super nintendo...etc....the name for the game you would play on the Emulator would be called a Rom. The Rom is the game which you are playing....like Final Fantasy 1...that's the Roms you would be playing on the Emulator......

Below are some screenshots of some Emulation from Gameboy Advance.