open hook refers to the fact that the hook is exposed and not buried into the body of whatever plastic lure you are using. For example when you texas rig a plastic worm the hook point is always buried so as to make the rig weedless.
When I texas rig i use a small bell sinker. I put the sinker up in the tube start the hooh through the top of the tube then go through the circle on top of the sinker then out the tube and finish in regular texas rig fashion. You get the best of both worlds: weedless and the spiral fall with the weight inside the tube.