collection - when the rider balances the driving (forward) and restraining aids on a horse. This causes the horse's frame to become compacted, the horse light on it's feet and supple in hand. The baseline is shortened, the shoulder is raised, the croup is lowered and the head is held on the vertical. The horse works off it's hind end, where it's hind end does much of the work.
So, lets see your collected horses. WP, Gaming, Dressage, Jumping, whatever, all types of horses.