In motion picture terminology, a tracking shot is the same as a dolly shot or a trucking shot--the camera is mounted on a wheeled platform that is pushed on rails while the picture is being taken. One may dolly in on a stationary subject for emphasis, or dolly out, or dolly beside a moving subject (an action known as "dollying with").
The tracking shot can be combined with other movements. If there is a crane mounted on the dolly, the camera can rise or fall while tracking. The camera can zoom and dolly at the same time. There are cases where an operator carrying a camera is dollied for part of the shot and then smoothly dismounts to continue the movement while walking.
With the invention of a harness called the Steadicam, which allows the operator to carry his camera while a set of counterweights damp the vibrations that would otherwise be caused by his walking or running, smooth hand-held work replaced dolly shots in many movies. Halloween was one of the first movies to use the Steadicam constantly.
Thus, some famous examples of tracking shots are actually Steadicam work, including Danny's point of view shots in Stanley Kubrick's The Shining, when wheeling around the Overlook Hotel; and the shot in the restaurant introducing several characters in Goodfellas ("And then there was Jimmy Two Times, who got that nickname because he said everything twice, like: I'm gonna go get the papers, get the papers.")
Dollies are still used when precise compositions and movements are desired. Elaborate dolly shots can be seen in the work of Max Ophuls and Samuel Fuller; each, in his own way, was interested in the duration of an event. Tracking allowed them to interpret an action through various compositions while filming continuously.
Tracking shots and Steadicam shots are both sometimes confused with zooms, but it should be noted that they typically look subtly different. A zoom simply magnifies part of the image by moving a lens within the camera; a tracking shot or Steadicam shot involves moving the entire camera. The difference in apparent position caused by the change in focal length will often be so subtle as to go unnoticed. For that reason, any shot showing parallax will typically not be the result of simply zooming in or out (though the camera operator may of course zoom in or out while tracking).
In the film Vertigo, the effects of changing focal length are apparent: the camera tracked in one direction while zooming in the opposite direction, causing an apparent "lengthening" of distance down the stairway. See Dolly zoom.
Studio mangling by superimposing credits and titles over the opening tracking shot in Orson Welles' Touch of Evil was not resolved until the fourth release of the film.