Détourné is a classical ballet term meaning “turned aside.” A dancer does a détourné by turning once completely around on both feet, on demi-pointe or pointe(for women on pointe of course). As the dancer turns, the feet position are reversed. So if the right foot was in front to start the détourné, it will finish in the back with the left foot front.
Détourné is done somewhat often in ballet classes and in ballets performed on stage. It is considered a basic step and could possibly be one of the first turns that a beginner will learn.