The tan sao is described as a palm up hand. It is an attacking hand oriented forward.
encyclopaedie
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.
As kwan sao, we describe a move composed of a tan sao and a deep bong sao. It is a defensive as well as an offensive move.
The gaan sao is a hand move that reminds of a plough. It moves downwards following the orientation line.