What action does "pushback" refer to in aviation?

"Pushback" in aviation specifically refers to the use of ground equipment to move an aircraft backward away from the gate. This process is essential as it allows the aircraft to clear the terminal area and start its taxiing phase towards the runway for departure.

During pushback, specialized vehicles, often called pushback tugs, are employed to ensure that the aircraft is safely and efficiently maneuvered without any risk of colliding with nearby structures or other aircraft. This action is critical to the overall flow of airport operations, as it sets the stage for the next phases of a flight, including taxiing and takeoff.

The other options do not accurately define pushback. "When the aircraft moves forward onto the runway" pertains to the takeoff phase, while "when the aircraft is repositioned for taxiing" does not specifically indicate the backward movement from the gate. Lastly, "the act of securing cargo before departure" refers to a completely different pre-flight procedure unrelated to the aircraft’s physical movement on the ground.