In cinematography, panning refers to rotating or pivoting a motion picture or video camera horizontally from a fixed position. This motion is similar to the motion a person makes when she turns her head on her neck from left to right. In the resulting image, the view seems to "pass by" the spectator as new material appears on one side of the screen and exits from the other, although perspective lines reveal that the entire image is seen from a fixed point of view.
The term panning is short for panorama, suggesting an expansive view that exceeds the gaze, forcing the viewer to turning her head to take everything in. Panning, in other words, is a device for gradually revealing and incorporating off-screen space into the image.
Panning should never be confused with "tracking" or "traveling," in which the camera is not just pivoted but is physically displaced left or right, generally by being rolled parallel to its subject.
https://en.wikipedia.org/wiki/Panning_(camera)