what does "have a hook" mean

Pretend the boat is rightside-up, the bottom curves up from the transom; it is "dished" forward of the transom. This "hook" will drive the bow down, reducing performance.

The bottom edge below the transom is lower than the rest of the bottom, some boats come like this from the factory, pantera's do not.

So since it's a pantera it probably doesn't unless it was grounded an repaired?

Or hanging off trailer bunks improperly.

Pantera 24s are not supposed to have hook. In fact they have a little rocker. But you would have to put a straight edge on the hull to see. No way to tell by looking at a boat go across the water.