Perhaps the best way to begin a guide to cruising is to define the difference between a ship and a boat. Roughly speaking, if a vessel sails on fresh water (lakes and rivers), it's a boat; if it sails on salt water (oceans or seas), it's considered a ship. In addition to those two broad categories, there are a number of other different kinds of passenger vessels that are appropriate for groups:
Barges--Small, self-powered riverboats. Generally, they are deluxe and serve gourmet food.