What is a horse's fastest pace?

The primary gaits are walk, trot, canter, gallop and run. Some people use the term gallop and run interchangably.

Traditionally, canter is a slower 3 beat gait and gallop or (hand gallop) is the faster version of a canter and still 3 beats.

In racing the fastest gait is 4 beats and the horse is said to be running.