“Shift” is the moving of a lens, up and down or to the sides, from its central position while retaining its perpendicular orientation to the film plane. Simply put, the adapter expands the diameter of the projected image circle at the film plane. This allows for much greater freedom in “placing” the image area within the now much broader circle before vignetting takes effect. And most importantly, all this happens without moving the orientation of the camera in relation to the subject. So if verticals, for example, are acceptable in the viewfinder, they will remain so whatever the amount of shift to include the “hidden” parts of the image. Simple but ingenious.
“Tilt” differs from shift in that the normal perpendicular orientation of the lens to the film plane is changed resulting in a change in the plane of focus. This means that at any given aperture/focus setting, the depth of field in the subject will not remain as simply the space between two measured points from the camera as is normally the case, but increased or decreased. This amount is user controlled. Once again, simple but ingenious.