When combining multiple images, it is critical that each image be captured from the same point of view. This optical center of the lens is commonly called the nodal point, although it is more correctly referred to as the rear entrance pupil. The nodal point is located inside the lens; in the wide angle lenses used for panoramic imaging, the entrance pupil tends to be near the front of the lens.
A standard tripod mount rotates the camera around the mounting screw in the camera; the simplest nodal point adapter simply shifts the camera back to move the lens's nodal point over the axis of rotation. More complicated brackets allow the camera to rotate vertically around the nodal point around the nodal point as well as horizontally.