As I've been taught, "Jao Sao" = "running hand"
Also sometimes referred to as "large disengagement" - "Huen Sao" being "small disengagement"
Granted, I'm not a JKD guy but I've trained with quite a few JKD guys in all sorts of settings and have had quite a bit of exposure to JF/JKD over the years.
In isolation, I've seen Jao Sao as this:
From right hand high reference point, person A drops his right hand down and around (the Jao Sao portion) while doing a Pak Sao with his left hand. A brings his right hand up for a hook or, more commonly, ridge hand toward the left side of B's head. If B blocks, the common response for A is a Jut Sao ("jerking hand") with a left strike low then a right strike high.
Mike