Fanny pack is an American name for a little pack carried around the waist. In UK it is called a Bum Bag. Fanny is slang for bottom in USA. Fanny is slang for female genitalia in UK.
It is believed that the American usage - first recorded somewhere between 1925 and 1930 - was influenced by the British usage (1879). Further ties place the origin of both words to the title character in John Cleland's erotic novel - the first of its kind - Fanny Hill (also known as Memoirs of a Woman of Pleasure).
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.
Some people still call them fanny packs. The accessory, which refers to a bag you can wear around your waist, is now also called a belt bag, waist bag, bum bag and hip bag.
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.
Tummy pack, belly bag, moon bag, belt bag, waist bag, butt pack, sling bag. People stress a lot over what to call them, but don't even worry! Just call it what you like.
Waist bags, bum bags, hip packs, slings, or crossbody bags. Whatever you call them, these bags are back and a must-have for travelers. Like a purse, a fanny pack carries all the small stuff you need for a day of sightseeing like your keys, external battery, and lip balm.