Overview
A waist bag, fanny pack, belt bag, moon bag, belly bag (American English), or bumbag (British English) is a small fabric pouch worn like a belt around the waist by use of a strap above the hips that is secured usually with some sort of buckle. The straps sometimes have tri-glide slides, making them adjustable in order to fit properly. It can be considered as a purse worn around the waist.
Although traditionally the bag was worn with the pouch at the front, the separate American and British names derive from the fact that they are often worn with the pouch above the buttocks, for which "fanny" and "bum" are respective slang terms in each country.
Early usage
Historically, the bag was positioned in front of the body, so people could protect themselves from bandits. Bags attached to belts have been in use since antiquity in many cultures. One origin was the Native American buffalo pouch which was used instead of sewing pockets into clothing. Buffalo pouches may also be worn on the wrist or carried on the front of the chest via a neck strap or lanyard. Ötzi had a belt pouch 5,000 years ago. The European medieval belt-pouch is another antecedent which was superseded as clothing came to have pockets. The Scottish sporran is a similar belted pouch that survived because of the impracticality of pockets in a kilt.
1950s and later
In 1954, a skiers leather fanny pack appeared in a Sports Illustrated Christmas shopping guide:
"$10. The lightweight leather 'fanny pack' is designed to hold a cross-country skier's wax and lunch. It's also useful for cyclists, hikers, equestrians."
From Wikipedia (CC BY-SA 4.0).