Dredge
Dredge is a static ability that functions only while the card with dredge is in a player’s graveyard. “Dredge N” means “As long as you have at least N cards in your library, if you would draw a card, you may instead put N cards from the top of your library into your graveyard and return this card from your graveyard to your hand.” A player with fewer cards in his or her library than the number required by a dredge ability can’t put any of them into his or her graveyard this way. See rule 502.47, “Dredge.”