What is the difference between lens shift and lens offset?

Vertical Lens Shift means that the image can be moved vertically of the total image height, above or below its original position.

 

Vertical Lens Offset describes how the top or bottom of the image offsets from the lens’s center line. Use the top edge of the image as a starting point and the lens centerline as reference. If the top edge of the image is 100% above the lens centerline, the lens offset would be 100%.