Positioning is the act of moving an aircraft from its current location to its departure point at any airport or leg of its journey other than the first. Positioning occurs when the aircraft has already departed its originating airport and landed at its first stop. From that point on, any time the aircraft leaves its gate and goes to the departure point is called positioning.
Though the term includes any point at which the aircraft is moving to its departure point, it is more widely used by air traffic control to instruct a pilot to move his aircraft off of the taxiway and past the runway hold line onto the actual runway itself. An air-traffic controller might instruct the pilot to "position and hold on the runway." This means that the controller wants the pilot to move the aircraft onto the runway and hold it there until cleared for takeoff. While holding short of the runway, a pilot can receive either a position and hold or position instruction from the controller, both meaning different things. When a pilot is cleared to position on the runway, the controller will most likely say "cleared for takeoff," making the instruction sound like this: "position 27L cleared for takeoff." This means the pilot is allowed to move his aircraft onto runway 27L and begin his takeoff roll.
Jet charter companies will use the term "positioning" to inform air traffic control that they are moving the jet to the departure end of the runway. This radio call is not mandatory but can be, if requested by a controller. Usually, the pilot of a charter will let the ground controller know that he is positioning as a courtesy due to the size, speed, and space requirements of the charter and its taxi. If a charter is requested to position and hold by a controller, then the pilot might respond with, "position and hold left," and is the pilot's way of letting the controller know he will be positioning himself left of the runway centerline to avoid any possible accidents if there might be landing aircraft.