Buyback was introduced in the Tempest block. It is used as a cost paid at the casting to return the spell to the caster's hand rather than the graveyard after the spell resolves.

702.24. Buyback

• 702.24a. Buyback appears on some instants and sorceries. It represents two static abilities that function while the spell is on the stack. "Buyback [cost]" means "You may pay an additional [cost] as you play this spell" and "If the buyback cost was paid, put this spell into its owner's hand instead of into that player's graveyard as it resolves." Paying a spell's buyback cost follows the rules for paying additional costs in rules 409.1b and 409.1f-h.

Rules Translation

• 702.24a. - You cast the spell, pay this cost, and then instead of having the spell placed in the graveyard on resolution return it to your hand. If the spell is countered it does go to the graveyard though.