From DominionStrategy Wiki
A stop card is any card that does not draw more cards. The term is typically used in the context of engines; such strategies usually aim to draw all or almost all of the deck each turn once the engine is running, so adding too many cards that don't draw—even the powerful payload cards that you do want in the deck, such as valuable Treasures or strong non-drawing terminal Actions—can get in the way of the engine's functioning.
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