Parallax

Parallax demo © Bernhard Vogl (GIF animation must be turned on)

If you shoot the same scene from a slightly different point of view the foreground will be shifted in relation to the background like in this example image.

Parallax occures in panoramic photography if camera and lens are not rotated around the Nodal Point of the lens and is visible in the overlap between two adjacent images.

Parallax errors are sometimes very hard to retouch since necessary background details might be obscured by foreground details. The only way to fix this kind of errors is to 'invent' some background details.