I used to think “prawn” was just another name for jumbo shrimp, but according to this – http://en.wikipedia.org/wiki/Prawn – they’re from a different sub-order entirely. Interesting, but does it make any difference when you’re cooking? Can you substitute shrimp for prawns, and vice-versa, in a recipe? (I don’t think I’ve ever actually eaten a prawn, nor seen one on the menu in an American restaurant.)
I think they’re pretty much interchangeable, unless size matters.