Push  is also 'Push Back.' An aircraft 'pushing' is usually quite literally a 'tug' or 'tractor' pushing the aircraft back from the terminal.

Aircraft can push back by reverse thrusting their engines, but that wastes a lot of fuel, it is extremely loud and it is easier to maneuver an aircraft by pushing it backwards as the crew in the cockpit cannot see backwards to steer themselves around other aircraft.

List of books: Push