Which term refers to the individual on a ride until they are unloaded?

The term that refers to the individual on a ride until they are unloaded is "Rider." In the context of amusement rides and attractions, a rider is a person who actively participates in the experience by being on the ride itself. This definition encompasses the full experience from boarding the ride, enjoying the experience while it operates, and finally being unloaded once the ride has concluded.

The other terms, while related to the context of ride safety and operations, refer to different roles or concepts. For instance, the operator is typically the individual responsible for running the ride and ensuring safety protocols are followed, while the participant can imply someone involved but not specifically on the ride itself. Restraint user could refer to anyone utilizing safety measures on the ride, which does not solely define the individual actively enjoying the ride experience as a rider does. Therefore, "Rider" is the most accurate term for someone present on a ride until they are unloaded.