The Game Genie is a series of cheat systems designed by Codemasters and sold by Camerica and Galoob for the Nintendo Entertainment System, Super Nintendo Entertainment System, Game Boy, Mega Drive/Genesis, and Sega Game Gear that modifies game data, allowing the player to cheat, manipulate various aspects of games, and sometimes view unused content and functions. It is known as the first example of consumer-friendly "game enhancement" by means of (temporarily) directly altering the binary code of a game.
Source: Wikipedia, "Game Genie", available under the CC-BY-SA License.