Definition - What does Detainee mean?
A detainee is a person that is being held against their will by law enforcement for a set period of time. The detainee may only be held until they are arraigned by a judge, or they might have already been sentenced to a set period of time. Any incarcerated person would be considered a detainee.
Justipedia explains Detainee
A detainee is not able to leave the place where they are being held by their own volition, and is only able to leave when law enforcement officials give them approval to do so. Detainees are normally held in secure areas from which they would be unable to leave, such as a jail cell.