Deck / Pool Building is a mechanism in which players start the game with a pre-determined set of cards / player pieces and add and change those pieces over the course of the game. Many deck-building games provide the players with a currency that they use to "buy" new items that are integrated into the deck or pool. These new resources generally expand the capabilities of the player and allow the player to build an "engine" to drive their future plays in the course of the game.

This mechanism describes something that happens in play during the game as a function of the game, not customization of the game from a body of cards prior to play.