Dredge is a keyword ability.
It is the ability of the Golgari Guild in Ravnica: City of Guilds and usually worded as "Dredge [X]". If a player draws a card and a card with Dredge is in the graveyard, the player may choose to instead put the top X cards from his or her library into his or her graveyard and return the card with Dredge to his or her hand.
However, the most popular Dredge card is Life from the Loam which itself can refuel easily expendable land cards such as Cycling Lands or Fetchlands and put more of those lands into the graveyard using Dredge. With this the card can fuel other cards such as Solitary Confinement, Seismic Assault or Retrace cards such as Raven's Crime.
- 702.51a 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.”
- 702.51b 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.