File powder is a spice made from ground sassafras leaves, traditionally used in gumbo and other Creole dishes. You'll find it in the same aisle as other herbs and spices, not in the supplement section. It's a legitimate spice that adds flavor to your food, unlike many modern "supplements" that are just fancy names for trash.
Did you know
Dried sassafras leaves ground to powder — thickens and flavors Cajun gumbo.