expansion pack

An expansion pack is an addition to an existing pen-and-paper RPG, game or video game. These add-ons usually add new game areas, weapons, objects, and/or an extended storyline to a complete and already released game. While board game expansions are typically designed by the original creator, video game developers sometimes contract out development of the expansion pack to third-party company, or it may choose to develop the expansion itself (see for Diablo). Board games and RPGs have been marketing expansions since at least the early 1970s.
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