Our digital cards are Non-fungible tokens (NFTs). NFTs are used to create verifiable digital scarcity, as well as digital ownership, and the possibility of asset interoperability across multiple platforms. NFTs are used in several specific applications that require unique digital items like crypto-gaming, crypto art, crypto-collectibles. If you want an easy-to-read-article about NFT, check out this one.
Every card we issue is unique, each card has unique characteristics (serial number, player name, season etc) backed by a unique NFT. For instance, the card of Cristiano Ronaldo Unique 2020-2021 is backed by this token (also referenced on his card page).