The Temporal Accord is an interstellar treaty regarding time travel, similar to Starfleet's Temporal Prime Directive. When time travel was first developed, all the major temporal powers agreed it would only be used for research. Some factions broke the accord, initiating the Temporal Cold War.
In an alternate timeline, in the early 25th century, Starfleet and the Klingons held the beginnings of time-travel technology in their hands. They imagined a possible "Temporal Accord" that would regulate the use of time-travel. (Star Trek: Phoenix-X: "Temporal Doom! Part II")