An older male with whom you associate as your adopted father. Teenage girls tend to have many father figures in their lives if they are lacking a father or have an issue with their own, actual father.
This also commonly leads to infatuation with older men who are father figures, be it theirs or in general.
Friend 1: Oh, I never had a decent father...
Friend 2: You have father issues?
Friend 1: Yeah. It means I now have a father figure...