With respect to the particular terms about which you asked:
“Dead or semi-dead release” Something to be avoided…seriously. It’s when your release hand does not move upon release, aside from your fingers opening. It’s generally indicative of collapsing at the shot or a lack of back tension. Ideally there should be a somewhat rearward movement in your release hand at the shot.
“Point-on distance” This is the distance at which you can hold the tip of your arrow on the bullseye like a sight pin and hit it.
“Gap shooting” At distances shorter than point-on, during aiming there will be a “gap” between the tip of your arrow and the bullseye. The tip will appear below the bullseye. Gap shooting is simply incorporating this knowledge into your aiming system. If you want some excellent tutorials on gap shooting I can provide you some links to various different types of gap systems by some of the best barebow archers in the nation.