Generally if it has thread along the whole length it is a screw, if it does not it is a bolt. But of course not everyone sticks to the naming convention.
I think the dark part in the screw illustration is a void as opposed to a screw point. If that is your query!.
Maybe more correct to call it a machine screw.
Generally if it has thread along the whole length it is a screw, if it does not it is a bolt. But of course not everyone sticks to the naming convention.