Are bald tyres non tread tyres?

Bald tyres are tyres where the tread has been worn of in use and if this is the case then the tyres are not same (and illegal) to use.

There are tyres made without a tread (for racing cars), these are not called bald tyres, they are called "slicks" and instead of a tread the surface of the tyre is made to be sticky in use.