The name derives from the fact that they are – I would like to think were – often worn with the pouch above the buttock, for which “fanny” and “bum” are the slang terms (thanks Wikipedia for this insight). I don’t get though, why you would wear the bag on your bum.
The fanny pack – or bum bag as the Brits would call it, since “fanny” is considered a vulgar word – is basically as we know it, a small pouch which can be leather or fabric, secured with a zipper, and worn by use of a strap around the waist.
As you know, building a wardrobe is a process. You have to tackle adding to your wardrobe with a strategy and direction, so you don’t end up with a bunch of random pieces that you struggle to wear or aren’t easy to mix and match.