Bolt or screw?

I had always use the partial plain shank for a bolt, and fully threaded for a screw, until a few years ago someone on the web said I was wrong and that a bolt screws into a nut and if it screws into something else it is a screw. When i thought about it this idea did have some merit, but if you are selling them the same thing might have its name determined by how you intend to use it, confusing.
No definition really works.
Partially threaded capscrews have already been mentioned.
Coach bolts might be partially or fully threaded, if you ask for a coach screw you will get one that screws directly into wood (a hefty wood screw with a square or now mainly hex head) not a fully threaded coach bolt.
For some jobs I use what I call gutter bolts, but more often roofing bolts. round slotted head and square nuts. I was given several boxes of then decades ago when an agricultural building constructor had a clear out from his van. These are fully threaded, but calling them screws would cause confusion as roofing screws are used to go directly into wood or steel, being self drilling.
If you ask the general public I suspect the most will call anything with a parallel thread and head a bolt.
But its clear that no definition really works. Perhaps like the Eskimos have hundreds of names for snow, we need more names for bolts / screws to avoid confusion. Probably why no descriptor is complete without a photo.
i really wrote the initial post to see what the language police thought.
Thanks for all of the contributions.