Payback was an act of reward or, likewise, retaliation for the actions of another, sometimes also known by the idioms "repaid in kind" or "responded in kind".
Following the capture of Captain Jonathan Archer and Sub-Commander T'Pol by rebel Coridans in October 2151, the Vulcan Sopek told Charles Tucker III he planned to take over the mission and send in an assault team. Upon hearing this, the protesting Tucker responded that, "You don't really care what happens to them, do you? You probably wouldn't mind if they got caught in the crossfire. You'd consider it payback for what happened at P'Jem." (ENT: "Shadows of P'Jem")
In 2374, Major Kira Nerys convinced Captain Benjamin Sisko to speak to Starfleet to help Quark acquire Keevan for a prisoner exchange for the Dominion-captured Ishka. Kira told Quark to consider payback for having her rescued from the station's holding cell, when the station was under Dominion occupation. (DS9: "The Magnificent Ferengi")