As Wiki says,
A non-fungible token (NFT) is a unit of data on a digital ledger called a blockchain, where each NFT can represent a unique digital item, and thus they are not interchangeable. NFTs can represent digital files such as art, audio, videos, items in video games and other forms of creative work.
Even after you buy an NFT object, it remains on the Internet: anyone can download it, print it and hang it on the wall, but you own the original. You can sell and purchase NFT objects on blockchain platforms – there are many of them. Some work as marketplaces with many categories, while others specialize, for example, in art or games. One of the popular sites is OpenSea.io
The highest price paid for NFT is $69.3 millions for Everydays: the First 5000 Days