Saddlebag

noun

1. One of a pair of pouches hanging across the back of a horse behind the saddle.
2. A pouch hanging from a saddle or over the rear wheel of a motorcycle or bicycle.
3. One of a pair of covered pouches, usually leather, laid across the back of a horse, donkey, or mule behind its saddle, or hanging over the rear wheel of a bicycle or motorcycle, frequently made of a rigid material.
4. The lateral fat on a person's upper thighs (in that case sometimes also known as "riding breeches") or buttocks, that hangs loosely, like saddlebags.
5. a large bag (or pair of bags) hung over a saddle