Multiple realities
(covers information from several alternate timelines)
(covers information from several alternate timelines)
A concubine was a woman in a relationship with a man with no prospect of marriage.
At the beginning of the Klingon Third Dynasty, a concubine named Karana was given the name and title of Shenara, daughter of Emperor Reclaw of the Third Dynasty. (DS9: "You Are Cordially Invited")
In 2153, Zjod attempted to sell Jonathan Archer and Malcolm Reed a "quite skilled" Nuvian concubine. (ENT: "Rajiin")
In the mirror universe, the Denobulan Phlox turned against Archer for the prospect of acquiring some concubines. Soval promised him he could choose as many as he wished. (ENT: "In a Mirror, Darkly, Part II")