These are also known as Non-fungible tokens. They are like digital assets associated to almost anything, like artworks, collectibles, sneakers, etc and especially online gaming where they represent in-game assets. Their ownership can also be transferred between individuals. The most common question is how to buy these NFT tokens.
NFT tokens can be traded in third-party market like MakersPlace. In the case of NFT tokens for in-game purchases, you don’t need the permission of the game developers to trade these tokens.
NFT tokens allow people to own digital items that they have bought or earned. The most common types of NFT tokens are ERC-721.