What is defined as block time in aviation?

Block time in aviation refers to the total time calculated from when the aircraft moves away from the departure gate (referred to as "moving off the blocks") until it arrives at the destination gate and is securely parked (which is known as "blocking in"). This includes the entire duration of the flight during which the aircraft is not at the gate, encompassing taxiing, time spent in the air, and taxi back to the gate upon arrival.

In this context, the other choices describe different aspects of aircraft operation but do not encompass the full definition of block time. For instance, the time spent in the air only accounts for the duration of the flight once the aircraft has taken off, while the period between takeoff and landing is limited to the flight's airtime and does not include ground operations before and after the flight. The duration of passenger boarding pertains solely to the boarding process and does not reflect the overall operational timeframe of an aircraft in service. Thus, defining block time as the period from when the aircraft moves off blocks until it blocks in to the gate encapsulates both airborne and ground activities, making it the most accurate choice.