http://www.perrysicecream.com/faq.html
Ice Cream - a frozen food made from a mixture of dairy products, containing at least 10% milk fat. Other ingredients are added for sweetening and flavor, such as fruits, nuts and chocolate chips. Ice cream must weigh a minimum of 4.5 pounds to the gallon.
Frozen Custard or French Ice Cream - contains a minimum of 10% milkfat, as well as at least 1.4% egg yolk solids.
Sherbets - have a milkfat content of between 1% and 2% and a slightly higher sweetener content than ice cream. Sherbet weighs a minimum of 6 pounds to the gallon and is flavored either with fruit or other characterizing ingredients.
Sorbet - similar to sherbet, but contains no dairy ingredients.
Frozen Yogurt consists of a mixture of dairy ingredients such as milk and nonfat milk, which have been cultured, as well as ingredients for sweetening and flavoring.
I was going to try to recite that shit off the top of my head, but I knew that I would get it all twisted, so Google once again wins.