Plain English Meaning
The people in the cockpit whose job is to actually fly and operate the aircraft.
Full Definition
Persons assigned to duty in an aircraft during flight time who are essential to its operation, including the pilot, copilot, and (when carried) flight engineer and flight navigator. Cabin crew such as flight attendants are not flight crewmembers under this definition.
Context Anchor
In the Sterile Flight Deck Rule, this term identifies the people on the flight deck who must avoid nonessential activities during taxi, takeoff, landing, and other high-workload phases.