A panoramic tripod head is a piece of photographic equipment, mounted to a tripod, which allows photographers to accurately shoot a sequence of images that can be used to produce a panorama, with minimum parallax problems.
A panoramic tripod head keeps the point of view of the camera stationary by placing it in the axis of rotation.
The purpose of a panoramic head is to allow you to accurately position your camera so that when you turn it you are turning it about the no-parallax-point of your lens. By rotating the camera around this point, you avoid parallax.
A panoramic head allows you to get the best possible pictures to produce the best possible panoramas and makes shooting the pictures much easier, and in a more systematic and, making it easier to stitch the pictures together afterwards.
To take a panorama, the camera is rotated at fixed angular increments, taking an image at each point. These images can then be assembled (stitched) using stitching software, which allows the images to be aligned and combined into a single seamless panoramic image.
How to avoid parallax
If everything in a scene is approximately the same distance from the lens, or very far away, the parallax effect will be eliminated or at least minimized. This is why hand-held panoramas from a mountain top tend to work quite well – everything is far away from the camera, and because the distances are very large compared to the tiny distance between the nodal point and the point of rotation, parallax is negligible.
Wide angle lenses can help reduce parallax effects because a wide angle lens accentuates perspective, making everything seem further away. However wide angle lenses also have a larger field of view so there is a greater chance that things in the foreground (including the ground itself) are captured and then cause problems. Providing there are no foreground objects juxtaposed against far away objects parallax will be minimized and you may be able to successfully post-edit any glitches in the stitch to achieve a good image. Conversely long focal length lenses compress perspective, exaggerating parallax effects.
The only way to eliminate parallax entirely is to use a panoramic head, which allows you to accurately position your camera so that when you take the pictures you are rotating the camera around the nodal point of the lens.