Starfleet Officer, Starfleet is made up of Commissioned and Non-Commissioned Officers. In some of the shows, mainly Voyager and Enterprise, they labelled the generic characters as Crewmen (even when some of them have rank)
Its the military today who get hung up between Officer and NCO(fficer) ranks and who gets called an Officer.
All enlisted personnel are not called NCO's. An NCO is an enlisted person that achives the E-4 grade in the Navy and E-5 grade in the Army. Enlisted personnel below that are not NCO's. That is probably why "crewman" in Starfleet is most likely similar to "seamen" in the Navy or "Private" in the Army.
That is why I disagree with the term "officers" as a catch all. That and most enlisted personnel hate to be mistaken for officers.