What is the parallax effect?
Parallax is a visual effect in which the camera is in motion and the foreground and background appear to move at different speeds. Either the background moves faster than the subject in front or opposite, depending on the camera setup, framing and focal length.
Video tutorial with sample shots:
For what is this technique being used in filmmaking?
A common way to use this camera technique in filmmaking is to put an actor or a subject in the center with the camera moving either 180° or 360° around the person.
Which type of camera gear is needed?
The parallax effect can be achieved by either using a dedicated camera slider that pans while moving from one side to the other, with a camera stabilizer or a gimbal which could even orbit the subject as well as with a dolly that is set up on a circular camera track.
The most dramatic effect can be achieved by using a tele-photo focal length. The motion effect can also be increased by putting a bigger distance between the foreground subject and the camera. But keep in mind that the background also needs to have a bigger distance towards the foreground subject.
Tips for getting the most out of the effect:
In general, it makes sense to try different focal lengths and distances between camera and subject to achieve the wanted result. A wide-angle shot can even be the better choice for slow movement due to the distortion of the lens. When filming with a wide field of view being close to the foreground subject is often more efficient than putting too much distance between camera and subject.