When someone rides on the back of a motorcycle, it is commonly referred to as being a passenger or riding pillion. The term "pillion" specifically refers to the seat behind the rider where the passenger sits. The passenger is also sometimes called a "backseat rider" or simply a "rider," although the latter term can sometimes be confused with the person operating the motorcycle. Regardless of the specific term used, riding on the back of a motorcycle as a passenger typically involves sitting behind the rider and holding onto handles or grips provided for stability and safety.