What we describe as jum sao is the sinking elbow. This minimal move protects the under part of the upper body like belly and liver.
encyclopaedie
Wu sao will be described as protecting hand. It is the last line of defense in front of the body, before the attack reaches it.
The scissors gaan sao is to be considered equally as defensive or offensive move. It protects the whole upper body from waist to head.
The gaan sao is a hand move that reminds of a plough. It moves downwards following the orientation line.