Rule 133.3.a
When characteristics are referred to in this way, it refers to any Game Object with the appropriate characteristic on the board, unless the zone is specified implicitly or explicitly by the effect doing the referring or the nature of the characteristic. Example: A "Yeti" refers to a game object with the Yeti tag on the board. Example: A "spell" refers to a spell on the chain, because spells cannot exist as game objects on the board. Example: A "spell in your trash" refers to a spell card in your trash because the effect specifies the zone in question.