Future Frieza is the alternate future version of Frieza.
In the alternate future timelines, Future Frieza and Future King Cold journey to Earth to destroy it in August of Age 764. Before they could even start their assault, Future Goku returns to Earth via Instant Transmission and successfully kills Future Frieza and Future King Cold. It was at this point that King Cold and Frieza had their DNA sampled by Future Dr. Gero's Remote tracking device for the creation of Cell.
While Future Frieza does not actually appear in Dragon Ball Z: Resurrection ‘F’, he is mentioned in one of Bulma's blog posts, where Future Trunks mentions that Future Frieza was never resurrected in his timeline.