A waist bag, also known as a fanny pack (US), belt, moon bag, belly bag (American English), bumbag (British English), is a small pouch made of fabric that is worn around the waist using a strap at the hips and secured with a buckle. Sometimes, the straps have triglide slides to allow for a custom fit. You can wear it around your waist as a purse.

The bag was traditionally worn with the pouch at its front. However, the American and British versions are distinguished by the fact that they are frequently worn with the pouch over the buttocks. For which "fanny", and "bum," are different slang terms. Fanny is a vulgar term for the vulva in the UK and Ireland. It is not used in Australia or elsewhere.