Sport boat?

Simple question:

What is a sport boat?
or
What is the 'definition' of sport boat?

Looking at them 'from a distance' I think I have gathered
that a J 24 is not a sport boat but both J 80 and  Melges 24
are. How come? Because they plane more readily?

How small can a sport boat be without becoming a dinghy?
How big? Is a Melges 30 still regarded as a sport boat?

Could a multuhull be a sport boat or is that too blasphemous?

Cheers,

-- 
Martin Schöön             "Problems worthy of attack
                           show their worth by hitting back."
		                                   Piet Hein