Haunt

Haunt is a keyword ability associated with the Orzhov guild from the Guildpact set in the Ravnica block. It works by allowing a permanent's "come into play"-ability (CIP) or a spell to go off twice. More precisely, it allows a card to be removed from a graveyard "haunting" another permanent, and when that permanent is put into a graveyard a triggered ability of the haunting card is put on the stack and allows a second usage of the card. Haunt appers only on black and/or white cards.

From the Comprehensive Rules:

• 502.51. Haunt
  • 502.51a Haunt is a triggered ability. “Haunt” on a permanent means “When this permanent is put into a graveyard from play, remove it from the game haunting target creature.” “Haunt” on an instant or sorcery spell means “When this spell is put into a graveyard during its resolution, remove it from the game haunting target creature.”
  • 502.51b Cards that are in the removed-from-the-game zone as the result of a haunt ability “haunt” the creature targeted by that ability. The phrase “creature it haunts” refers to the object targeted by the haunt ability, regardless of whether or not that object is still a creature.
  • 502.51c Triggered abilities of cards with haunt that refer to the haunted creature can trigger in the removed-from-the-game zone.