A palfrey is a type of horse that was highly valued as a riding horse in the Middle Ages. It was a lighter-weight horse, usually a smooth gaited one that could amble, suitable for riding over long distances. Palfreys were not a specific breed as horse breeds are understood today.
The word "palfrey" is cognate with the German word for a horse (of any type), pferd. Both descend from Latin, paraveredus, meaning a post horse or courier horse. The German term for a palfrey, meanwhile, is Zelter, which literally means ambler and is cognate with the Icelandic, tölt.
A palfrey usually was the most expensive and highly bred types of riding horse during the Middle Ages, sometimes equalling the knight's destrier in price. Consequently, it was popular with nobles, ladies, and highly ranked knights for riding, hunting, and ceremonial use.
The significant characteristic of the palfrey was that, rather than trotting, it usually possessed a smooth, ambling gait. The amble was the name given to a group of smooth, four-beat gaits faster than a walk, but slower than a canter or gallop. The trot is a two-beat gait, about 8 mph, suitable for covering a lot of ground relatively quickly. However, the horse also has a bit of a spring in its motion as it switches diagonal pairs of legs with each beat, and thus can be rough for a rider, and the trot also jostles about packs or weaponry to a considerable degree. The amble is about as fast as the trot, not tiring for a horse that performs it naturally, and much smoother for the rider. Thus, because much ground transportation in the Middle Ages was on horseback, with long distances to be covered, a smooth-gaited horse was much desired.