A Collaborator is an individual who works with enemy forces against one's own people.
During the Occupation of Bajor, a number of Bajorans worked in the Bajoran Cooperative Government as collaborators with the Cardassians. Kubus Oak and Basso Tromac were two men who worked in the government for the Cardassians. Following the end of the occupation all Bajorans who had worked with the Bajoran Cooperative Government were sentenced to exile. (DS9 episodes: "The Collaborator", "Wrongs Darker Than Death or Night")
A well known Bajoran collaborator was Amkot Groell, who ran the Okana Shipyards on Bajor, having convinced the Cardassians that he was running a museum. Following the end of the occupation he was allowed to continue living on Bajor and running the shipyard, which had received a commission from Starfleet to build the Ambassador class USS Hannibal. Amkot was blackmailed into cooperating with the remnants of the Alliance for Global Unity by members who had escaped arrest into attempting to assassinate Commander Benjamin Sisko and Major Kira Nerys. After the Hannibal was completed Amkot committed suicide. (DS9 novel: Antimatter)
In 2365, a Bajoran named Vaatrik served as a direct link between Gul Dukat and at least eight Bajoran sympathizers. Kira was sent to find the identies of the other collaborators that Vaatrik had worked with. Vaatrik walked in unexpectedly and Kira was forced to kill him in self defense. (DS9 episode: "Necessary Evil")
Baras Rodirya was a collaborator working for Gul Pavok on the planet Jevalan who managed to infiltrate the Bajoran Resistance. In 2369, after an attack on the Olanda labor camp he and fellow resistance member Ishan Anjar were arrested by the Cardassian Guard. Baras then gave the necessary code to the Cardassians to convince them that he was working with Pavok. Ishan was soon executed, and Pavok switched the identities of the two Bajorans, telling the Bajoran population that Baras Rodirya was dead. After escaping from custody, Baras killed the two witnesses that could possibly identify him as Baras. In the aftermath of the occupation Baras maintained the Ishan Anjar identity, and used that to launch a political career both on Bajor and within the United Federation of Planets. After arranging the assassination of Federation President Nanietta Bacco, Baras arranged to be named as President Pro-Tempore of the United Federation of Planets until a Special Election could be held. In October, 2385, the deception was finally uncovered. Baras was arrested and removed from power. (ST - The Fall novel: Peaceable Kingdoms)