Rebound is a keyword introduced in Rise of the Eldrazi and appears on instants. If the spell was cast from hand, it is exiled as it resolves. At the beginning of its controller's next upkeep, the player may cast it again without paying its mana cost.
Reminder text
The latest reminder text for Rebound reads: Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)