Cajun is a corruption or abbreviation of "Acadian" -- it refers specifically to the people of French ancestry who fled Nova Scotia (formerly Acadia) when the British defeated the French. Sorry, don't have the date at my fingertips, but this happened well after Louisiana had become an established French colony.

These refugees from maritime Canada were seeking a new French-speaking homeland, and many of them found their way to the swamps and prairies of southwest Louisiana, where they preserved their language and unique culture well into the 20th century.

Not all Louisianans of French ancestry and/or culture have been Cajuns -- the term refers specifically to members of this originally isolated rural community with its own unique music, rustic cuisine, etc.

The word "Creole" comes from the Spanish "crillo," which originally referred to the first generation born in the "New World," offspring of settlers from Europe (Spain or France). It has come to mean different things to different people; the most controversial aspect of the various debates is probably whether the term "Creole" refers to white or to black/mixed-race people. (Way back during the days of that first generation of American-born "Creoles," there may have been disagreement over whether the term was restricted to kids with two white parents, as opposed to those born to a Frenchman and an African or Native American woman.) You'll find staunch proponents of one interpretation to the exclusion of the other, plus plenty of us who accept "either/or."

Whether referring to Caucasians or colored folk, the adjective "Creole" usually connotes a more urban, aristocratic, and/or sophisticated cultural quality than the funky down-home "Cajun."

One very common meaning for "Creole" refers to the New Orleanian population of light-skinned black folks (most of them no more than 1/16 or 1/32 African) whose ancestors were never slaves and who maintain their own little elite society to this day.

Another meaning for "Creole" refers to any and all French-speaking black people of southwest Louisiana, the community that developed Zydeco music. Unlike most of the other meanings, "Creole" in this context has absolutely no connotation of urbanity or aristrocracy. These Creoles come in all shades of brown and black, including pure African blue-black, and they're farmers, not city folk. Of course, their numbers do include royalty, such as Clifton Chenier, the late great King of Zydeco.

A couple of us debated meanings of these terms in another recent thread on this same song, along with a few other questions and opinions brought up by the lyrics -- you might be interested.