A consul was an official appointed by a government to reside outside the government's territory and oversee that government's interests and provide assistance to its citizens abroad.
Consuls were among the highest officials in the Romulan Senate. Admiral Valdore promised Senator Vrax that he would be First Consul in the Senate. (ENT: "The Aenar")
In 2287, General Korrd was the Klingon consul to the Planet of Galactic Peace. Starfleet Operations also considered Federation representative St. John Talbot and Romulan representative Caithlin Dar as consuls. (Star Trek V: The Final Frontier)
In 2366, when DaiMon Goss represented the Ferengi Alliance in the bid for the Barzan wormhole, he identified his subordinate officers Arridor and Kol as consuls. (TNG: "The Price")
In 2373, Captain Kathryn Janeway and Neelix dealt with a Tak Tak consul during a three-day trade mission, who later planned to destroy USS Voyager when he learned that it had been infested with macroviruses. (VOY: "Macrocosm")
In 2375, Burkus served as the Deputy Consul of the Monean Maritime Sovereignty. (VOY: "Thirty Days")