Most people think it means putting the muzzle of a gun right on the target to be shot. This is point blank but there is more to the term.
What point blank means is that when the bullet is fired at the target there is no adjusting the elevation of the weapon used. If a target is a long distance away, the shooter has to factor in how the bullet will drop slightly during flight.
We get the term point blank from the French. Long ago, the center of a target was a small white circle. Since the French word for white is blanc, one strived to hit this white spot.