Emulators are programs that allow one type of game to be played on another system. Such as a PS2, or PSP native game being able to be played on a PC. While not just for video games, they can be used for other purposes. Some parts of emulating setup is prohibited under law such as obtaining copies of BIOS (Basic Input Output System) unless these were purchased legally. Emulating is regularly a complex thing to like like modding a console game system.