What is a small flat leather case for papers and paper money?

A small flat leather case for papers and paper money is called a wallet. Wallets are usually carried in a pocket and are used to store paper currency, credit cards, identification cards, and other small items. Wallets can be made from different materials, such as leather, fabric, or synthetic materials. They come in various sizes and designs, and can be customized with different colors, patterns, and details. Some wallets also feature additional features, such as coin pockets, card slots, or a checkbook holder.