As for the actual difference between a Shrimp and a Prawn, this (PDF) gives a fairly good explanation. Most of the time I refer to a Prawn as a larger Shrimp, which is not always correct. For the most part the words are synonymous. However, the shrimp that is sometimes ordered on a pizza, or popcorn shrimp (breaded, fried shrimp) are, in fact, shrimp. What was I talking about? Bah! All I know is they are good. :P