How many beats in a horse's gallop?

The trot is a two-beat gait. This is because the horse's feet hit the ground in pairs, so you hear two separate noises before the horse is back where it started. The trot is usually diagonal (off hind and near fore, then near hind and off fore.) Some horses, usually harness racers, move their feet in lateral pairs (off hind and off fore, near hind and near fore.) This is usually called pacing instead of trotting. It is also a two beat gait.