Prisoner Transporter is a type of Spaceship used to transport criminals.
Whenever a criminal or smuggler is caught in the Quintar Alignment, they are immediately escorted into a Prisoner Transporter, and then transported to the Detention Facility Trion-Alpha on Penetera.
Vala's team was caught and escorted on one of these ships into the prison on Penetera. (SG1: "Vala Mal Doran 2")