There are a couple of different schools of thought on this one. First, the general rule is that any type of soup that includes potatoes can be called chowder.  To take that a bit further, chowder can be any soup that is thick and chunky. Chowder is less chunky than stew, but has more ingredients in it than a typical soup. Clam Chowders, Southwestern Corn Chowders, and other seafood chowders are the most typical types, but chowder can be made from any combination of vegetables and or/meat.