"Hound" is a synonym for "dog", also used in a more specific sense to refer to a type of dog used by hunters to track or chase prey. Hounds can be contrasted with gundogs, which assist hunters by identifying the location of prey and/or recovering shot quarry. The hound breeds were the first hunting dogs. They have either a powerful sense of smell or great speed.
There are three types of hound, with several breeds within each type:
Sighthounds (also called gazehounds), which follow prey predominantly by speed, keeping it in sight. These dogs are fast and assist hunters in catching game—fox, hare, deer and elk.
Scenthounds, which follow prey or others (like missing people) by tracking its scent. These dogs have endurance but are not fast runners.
The remaining breeds of hound follow their prey using both sight and scent; difficult to classify as they are neither sighthound nor scent hound.
This may not include all hound-type dogs. The international kennel club association, the Fédération Cynologique Internationale, does not have a Hound Group and includes most hound-type dogs in Group 6, Scenthounds and related Breeds, and Group 10, Sighthounds.