ERC-721 is the standard used for non-fungible tokens (NFTs) on the Ethereum blockchain. Unlike ERC-20 tokens, which are interchangeable and identical to one another, ERC-721 tokens are unique and cannot be exchanged for one another.

ERC-721 tokens are often used to represent digital assets, such as collectibles or artwork. Each ERC-721 token has its unique identifier, making it possible to track ownership and transfer of the token on the blockchain.

Polygon is an EVM-compatible blockchain that also supports ERC-721 tokens. This means that NFTs created on the Ethereum blockchain using the ERC-721 standard can also be used on Polygon. Many NFT marketplaces, including the artstrid.com platform, offer the option to buy ERC-721 tokens on the Polygon network.

Overall, ERC-721 tokens offer a unique way to represent and exchange ownership of digital assets. Whether you're a collector or an artist, there are plenty of ways to use ERC-721 tokens on the Ethereum blockchain and beyond.