The canter and gallop are variations on the fastest gait that can be performed by a horse or other equine. The canter is a controlled three-beat gait, while the gallop is a faster, four-beat variation of the same gait. It is a natural gait possessed by all horses, faster than most horses' trot, or ambling gaits. The gallop is the fastest gait of the horse, averaging about 40 to 48 kilometres per hour (25 to 30 mph). The speed of the canter varies between 16 and 27 kilometres per hour (10 and 17 mph) depending on the length of the horse's stride. A variation of the canter, seen in western riding, is called a lope, and is generally quite slow, no more than 13–19 kilometres per hour (8–12 mph).

Since the earliest dictionaries there has been a commonly agreed suggestion that the origin of the word "canter" comes from the English city of Canterbury, a place of pilgrimage in the Middle Ages, as referred to in The Canterbury Tales, where the comfortable speed for a pilgrim travelling some distance on horseback was above that of a trot but below that of a gallop. However, a lack of compelling evidence made the 18th-century equestrian Richard Berenger remark in The History and Art of Horsemanship that "the definition must certainly puzzle all who are horsemen and all who are not" [author's italics], and suggest his own derivation, noted in contemporary dictionaries, from the Latin word cantherius, a gelding, known for its calmness of temper.

The canter is a three-beat gait, meaning that there are three hoofbeats heard per stride. Each footfall is the "grounding" phase of a leg. The three footfalls are evenly spaced, and followed by the "suspension" phase of the gait, which is when all four legs are off the ground. The three beats and suspension are considered one stride. The movement for one stride is as follows:

The canter and gallop are related gaits, so by asking the horse to gallop from a canter, the rider is simply asking the horse to lengthen its stride. When the stride is sufficiently lengthened, the diagonal pair of beat two breaks, resulting in a four beat gait, the inside hind striking first, before the outside fore. A careful listener or observer can tell an extended canter from a gallop by the presence of the fourth beat.

The gallop is the fastest gait of the horse, averaging about 40 to 48 kilometres per hour (25 to 30 mph), and in the wild is used when the animal needs to flee from predators or simply cover short distances quickly. Horses seldom will gallop more than 1.5 or 3 kilometres (0.93 or 1.86 mi) before they need to rest, though horses can sustain a moderately paced gallop for longer distances before they become winded and have to slow down.

Although the walk, trot, and canter can be collected to very short, engaged strides, the gallop if collected will turn back into a canter. The "hand gallop" of the show ring is not merely an extended canter, but a true lengthening of stride, yet still fully under control by the rider. A racing gallop, in contrast, pushes the horse to the limits of its speed.

The fastest galloping speed is achieved by the American Quarter Horse, which in a short sprint of a quarter mile (0.40 km) or less has been clocked at speeds approaching 55 miles per hour (88.5 km/h). The Guinness Book of World Records lists a Thoroughbred as having averaged 43.97 miles per hour (70.76 km/h) over a two-furlong (0.25 mi or 402 m) distance in 2008.

The "lead" of a canter refers to the order in which the footfalls occur. If the left hind leg is placed first (beat one), which would then be followed by the right hind and left foreleg (beat two), before the right foreleg (beat three), the horse is said to be on the "right lead". If the right hind leg is beat one, then the left foreleg will be the last leg to ground, and the horse will be said to be on the "left lead". Therefore, a person on the ground can tell which lead the horse is on by watching the front and rear legs and determining which side the legs are literally "leading", landing in front of the opposing side.