A "Sims 2: Double Deluxe" registration code is the serial number that comes with the copy of the game. It is normally located on the back of the jewel case or with the registration instructions.
The registration code is required to play the game, and it unlocks online features such as game patches and updates. The "Sims 2: Double Deluxe" is a life-simulation video game developed by Maxis, and was later on acquired and published by Electronic Arts. It is for gamers new to the series, and a good gift for the friend that has been toying with the idea of buying "The Sims 2."