A Gainer Flip is a back flip that travels forward.
If your dog lands closer to you than they started on your flips then your dog is gainering.
Disc dog flips are all variations of a back flip. Dog looks up and back and the feet come up in front of the dog. If the landing point of the Flip is in front of the take off point, then that is a Gainer Flip. Most Gainer Flips land with your dog facing in the opposite direction from which they started.
The movement of Gainer Flips makes for some creative trick, pattern, and sequencing opportunities.