Cavalry (from the French cavalerie, cf. cheval 'horse') or horsemen were soldiers or warriors who fought mounted on horseback. Cavalry were historically the most mobile of the combat arms. An individual soldier in the cavalry is known by a number of designations such as cavalryman, horseman, dragoon or trooper. The designation of cavalry was not usually given to any military forces that used other animals, such as camels, mules or elephants. Infantry who moved on horseback, but dismounted to fight on foot, were known in the 17th and early 18th centuries as dragoons, a class of mounted infantry which later evolved into cavalry proper while retaining their historic title.
Cavalry had the advantage of improved mobility, and a man fighting from horseback also had the advantages of greater height, speed, and inertial mass over an opponent on foot. Another element of horse mounted warfare is the psychological impact a mounted soldier can inflict on an opponent.
The speed, mobility and shock value of the cavalry was greatly appreciated and exploited in armed forces in the Ancient and Middle Ages; some forces were mostly cavalry, particularly in nomadic societies of Asia, notably the Mongol armies. In Europe cavalry became increasingly armoured (heavy), and eventually became known for the mounted knights, during the 17th century cavalry in Europe lost most of its armor, ineffective against the muskets and cannon which were coming into use, and by the mid-19th century armor had mainly fallen into disuse, although some regiments retained a small thickened cuirass that offered protection against lances and sabres and some protection against shot.
In the period between the World Wars, many cavalry units were converted into motorized infantry and mechanized infantry units, or reformed as tank troops. However, some cavalry still served during World War II, notably in the Red Army, the Mongolian People's Army, the Royal Italian Army, the Romanian Army, the Polish Land Forces, and light reconnaissance units within the Waffen SS. Most cavalry units that are horse-mounted in modern armies serve in purely ceremonial roles, or as mounted infantry in difficult terrain such as mountains or heavily forested areas. Modern usage of the term generally refers to specialist units equipped with tanks ("armored cavalry") or aircraft ("air cavalry").