Crewman refers to the lowest three enlisted rates of the Federation Starfleet, followed by the Petty Officer ranks. The rank is higher than a Crewman Apprentice and lower than a Petty Officer Third Class. It is the third enlisted rank. Personnel having this rank are referred to simply as Crewman.
The Ferengi Alliance Defense Fleet also used the rank of crewman. Crewman was in fact their only enlisted rate, and seniority was based on time served and profit earned.