A dragoon is a soldier trained to fight on foot, but transport himself on horseback. In other words, they move as cavalry but fight as infantry. The name derives from their primary weapon, a carbine or short musket called the "dragon."
Dragoons were organized not in squadrons but in companies, like the foot, and their officers and non-commissioned officers bore infantry titles. However, dragoons were at a disadvantage when engaged against true cavalry, and constantly sought to improve their horsemanship and armament to the cavalry standard. Thus, "dragoon" came to mean medium cavalry by the time of the early wars of Frederick the Great.
The term "to dragoon" dates from the earlier mounted infantry period. Dragoons were the most efficient and economical form of cavalry for police work and guerrilla warfare.