Which of the following best defines the term "pilot in command"?

The term "pilot in command" refers specifically to the pilot who is responsible for the operation and safety of the flight. This individual has the ultimate authority over the aircraft and the responsibilities associated with it, including making all operational decisions and ensuring compliance with safety regulations.

The pilot in command may vary from flight to flight based on a number of factors including qualifications and experience, but it is this direct and overarching responsibility for safe operation that defines their role. Being charged with the safety of the passengers, crew, and aircraft makes this designation critical in aviation.

While factors like flight hours, who files the flight plan, or who is assigned by the airline might play a part in a flight operation, they do not encapsulate the core essence of the pilot in command's responsibilities. Thus, the focus on the specific role and accountability for the flight effectively illustrates the definition of a pilot in command.