Creole mustard is a coarse-grain, vinegar-forward prepared mustard associated with Louisiana cooking, made by macerating brown or oriental mustard seeds in vinegar rather than grinding them fine.
Its exact origin isn't well documented, but it's believed to have developed as Creole cooks adapted French-style mustard to local ingredients and tastes. It's sharper and more pungent than yellow mustard, with a coarse, seedy texture.
It's used as a condiment (notably on po'boys), stirred into marinades, and worked into dressings and sauces such as remoulade for Creole and Cajun dishes.