Gumbo is basically a stew. Some would say it's a seafood stew, but it doesn't always contain seafood. There are gumbos made with sausage and venison and other meats as well. Gumbo was not originally just a name for a stew. "Gumbo" came from "gombo", which was an African word for "okra." Originally, "Gumbo" was a stew that contained okra as a thickening agent. Okra was only avaliable at harvest time, when the ripe pods appeared on the plant. The solution to have gumbo year round was to find a substitute thickener for times when okra was not available. That solution came from the Choctaw Indians who inhabited the north side of Lake Pontchartrain. The Indians made their stews with powdered sassafras leaves(filé) as a thickener, which was available all year round. Thus "filé gumbo" was born. Some gumbo recipes call for okra and some call for powdered sassafras, or "filé powder," and there are some that are still called "gumbo" or "filé gumbo" although they contain neither ingredient. The key here seems to be rice and seafood.
Gumbo recipes on this site:
Friendship House Seafood Gumbo
Bill Martin's & Zuider Zee's Gumbo
Phaed