Some of the best-known ballet steps and movements are the pirouette, plié, brisé and chassé. These terms, like most of the words used in ballet terminology, are French. The website of the American Ballet Theatre provides a dictionary of ballet terms and includes descriptions of ballet steps and movements.
Using these examples, a pirouette is a complete turn of the body on one foot. A plié is bending of the knee or knees. A brisé is a small beating step with a broken movement. A chassé is a series of steps in which one foot chases the other foot out of its position.