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.
encyclopaedie
Man sao is the searching hand. It serves as front line to take the first attacks of the opponent. The typical ving tsun guard position is man sao...
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.