We’re in the Black Lightning universe. If there’s ever a crossover, Supergirl will come to Freeland, or Green Arrow will come to Freeland.
Arrow, Flash and Legends all center largely around “Earth-1,” while Supergirl was established as “Earth-38,” and Black Lightning has no such designation.
In the meantime, Black Lightning will air its first season finale tonight, the trailer for which you can find below.
Black Lightning got fan hopes up when it started namedropping Supergirl and Arrow characters, but don’t expect Jefferson Pierce or his daughters to fight aliens just yet.