Biologically speaking, Crustaceans is a term used to describe the largest group of marine anthropods. Anthropoda are a classified under the Phylum taxonomic rank. (YG's brain hurts now from all that biology so if you are desperate to know more, here is the Wikipedia on Biological Classifiation).
One of the major classes within the Crustacean group is the Malacostracans which contains lobsters, crabs, shrimps and prawns.
All YG can say is YUM, we love eating all sorts of malacostracans so we've found some links you might be interested in: