It's a technique where you moderately accelerate to about 40MPH, then feather the throttle to put the car in the glide state. That's where there's no arrows on the display. The car's in the hybrid equivalent of neutral, where the only energy being used is to power the car's electronics. You then glide down to 30MPH or so, then accelerate back up. Using this technique, some guys got 110MPG out of a single tank, in a Prius, last August.

Obviously, you can only P&G where traffic conditions allow it. You don't need to do both, either. Once you get the hang of gliding, you'll find lots of places to use it. From your first post, it sounds like you're using the electric motor at times where you could glide.

I've never driven a HH, but I've heard the glidingg technique is not as easy to do, as in a Prius. You also won't glide as well, but it's worth a try.