An ERC-721 is an Ethereum-based token is a unique and non-interchangeable unit of data stored on a digital ledger. It represents proof of ownership of either a tangible or intangible asset.
An Ethereum Request for Comments 721 (ERC721/ ERC-721) token is a type of Non-Fungible Token (NFT) that is built on the Ethereum blockchain. Although these are a form of blockchain contract, it is the data that they represent that gives it its value. Some use cases include video games, art, property and other resources. As with cryptocurrencies, these contracts are generally stored either in a crypto wallet or on a dApp.
Their main use is to create unique digital items whose ownership is encrypted and therefore more secure than other digital assets might be. Two famous implementations include the first-ever blockchain-based TCG game, Spells of Genesis and the trading/breeding cat-game CryptoKitties. In the case of Spells of Genesis, it was originally based in directly on the Bitcoin blockchain and then moved to Ethereum later, as EverdreamSoft felt that it would be more secure. But it uses a combination of in-game and blockchain-based cards.
On the other hand, CryptoKitties is based on the premise that each CryptoKitty is as unique as the token that it represents. This is assured through the programming of the smart contract protocol of the CryptoKitty token. As the potential for blockchain and NFT technology becomes more apparent, more and more companies and high-profile individuals are also developing new uses for them. For instance, Coca-Cola is attempting to implement an NFT token to track its production, distribution and sales of products.