The term "Cab" in snowboarding generally refers to any switch-Front spin (no matter what the amount of rotation) on any feature (halfpipe, jumps, rails, boxes). For example, a "switch-backside 1080 double cork" off a jump would be referred to as a "cab 1080 double cork". The term was originally only applied to a switch-backside 360 in a halfpipe in which a rider would take off a wall switch, spin 360 degrees backside, and land on his/her comfortable stance (regular/goofy). Therefore the term "Cab" only applied to tricks in the halfpipe in which rotations were in full 360 increments, such as a "Cab 360" or "Cab 720." For example, since a switch-backside 540 would land a rider in the same switch position he/she took off from in the halfpipe, it was not referred to as a "Cab 540" because the rider dide not take off switch, spin backside, and land in his/her comfortable stance.
Thanks to Schmidhalter Michel for the video