There is a vast world of ambiguity out there. In fact ambiguity is an understatement. Different groups of decorators call all these different products by interchangable names.
As an aside my daughter seems to have hundreds of friends who share maybe a handful of names so I never really know who she's referencing same principle but I digress.
Just try nailing down the definitions online even, much less from book to decorating book. I would quote some books but we are still painting (aghhh!!) and those books are in boxes.
But I mean just look at the handful of conflicting responses you've already received. Trust me everybody calls it different--no kidding.
Just some 'depends on which way the wind is blowing' thoughts for you.
Okay here is what I have read. Fondant and sugarpaste are the same. Gumpaste and flower paste are the same. Modeling paste and fondant that has tylose/cmc added to it are the same.
Jessica 
if you have any instructions/books from the UK, AUS and RSA, fondant is called sugarpaste and gumpaste is called flowerpaste in these countries modelling paste usually stays modelling paste
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