The rules that define Gwent or a card within the game.
The foundation of any CCG, or game for that matter, are its mechanics. A difference must be made between card and game mechanics. The latter describes the basic tools and restrictions of the game; in Gwent, these are e.g. passing, row placement, or mulliganing.
Card mechanics are defined by card abilities then activated through the playing of a card. Examples of such mechanics are revealing a card or consuming a unit. Some mechanics, either game or card, may be defined as keywords within the game.