Dredge

‘Dredge’ was introduced in the Ravnica Block and it currently appears on a number of cards such as Life from the Loam

702.49. Dredge

• 702.49a. 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.”
• 702.49b. 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.

Translation:

• 702.49a. Dredge is always active, but when you would draw a card you can instead move N cards from the top of your library to your graveyard to return this card to your hand.
• 702.49b. If you don’t have enough cards in your library you can’t Dredge a card.