A pack-in game is a game that is included with the purchase of a video game console. It is a form of product bundling.
Pack-in games are generally intended to be desirable enough to help sell the system, and make good use of its positive features. Sometimes a pack-in game will be changed to a more popular game, or another game will be added, along with the original pack-in, if it is perceived that a newer game will sell more systems. Pack-in games are often the most plentiful games at used game shops.
In the case of Super NES, Super Mario All-Stars was added as a free mail-in offer. Other systems have included pack-in games on a built-in chip, such as Solitaire for Game.com.