For the DS9 episode, please see The Passenger.
A passenger was a person who traveled aboard a vehicle but was not active in its operation nor a part of the crew.
In 2366, the starship USS Enterprise-D was ordered to take Tam Elbrun, a mission specialist, as a passenger. (TNG: "Tin Man")
In 2381, Brad Boimler told Beckett Mariner that he saw himself as a "natural passenger," as he thought that driving was "scary." (LD: "Mining The Mind's Mines")