Wiktionary
n. (context bullfighting English) A mounted bullfighter whose task is to provoke the bull
Wikipedia
Rejoneador (, pl. rejoneadores; "lancer") is the name given to a bullfighter who fights the bull on horseback. The rejoneador should not be confused with the picador, who is just an assistant of the matador. The rejoneo is a form of bullfighting in Portugal and in Spanish bullfighting.
Classic bullfights may also exhibit a rejoneador spectacle preceding the main event but if the corrida is made up exclusively of rejoneadores, it is called a rejoneo or corrida de rejones. Corridas mixtas are also popular, where a rejoneador and two matadors (or a rejoneador, matador and novillero—an apprentice matador) perform.
The point of the bullfight is to demonstrate the skill and nerve of the rider in controlling both the bull and the horse.