An expansion is an addition to an existing Board or Card game. These add-ons usually add new content to a complete and already released game. Please use the game's own tag as well, and consider using the tag specific to the expansion itself (if it exists).
An expansion pack, expansion set, or supplement is an addition to an existing Board or Card game. These add-ons usually add new game areas, weapons, objects, and/or an extended storyline to a complete and already released game.
As expansion packs consist solely of additional content, most expansion packs require the original game in order to play. Although another expansion packs, called stand-alone expansion packs, do not require the original game in order to use the new content.
(from Wikipedia)
Please use the game's own tag as well (e.g. catan), and consider using the tag specific to the expansion itself (e.g. catan-seafarers) if it exists.
