One of the core moves of the Wing Tsun curriculum, this technique roughly translates to "Sensing Arm." This is separate from Man Sao, or "Searching Arm," which is the forward hand in the fighting stance, although the two arm postures bear similarity and are, application-wise, tangled together like the roots of two ancient trees.
As with all Wing Tsun movements, this is often called a technique, but it is actually a principle. Traditionally, in Chinese martial arts, "techniques" have more flowery and descriptive names like, "Violently Sauced Buddha Begs for Alms Whilst Searching for Car Keys in Fannypack."
And being a principle, Fuk Sao, like other Wing Tsun principles, will often confuse beginners or the uninitiated by appearing in multiple shapes. The Fuk Sao of the Siu Nim Tao form, for instance, places the elbow at the center-line and fingers and palms facing back towards the stylist, like a hook. In comparison, the Fuk Sao of the Chum Kiu form places the elbow slightly off-center. The palm and fingers are all pointed rigidly ahead. Both of these techniques are Fuk Sao. Both are an application of "Sensing Arm." | 
