Difference between the short and long shank machines.
If the part of the foot that can be removed from the pressure bar (unscrew the whole foot) is 'short' that is a short shank (about 1/2 inch in height), if it is taller (about 1 inch in height) it is a long shank. A slant shank actually 'leans' backwards instead of straight up.
Does this help?