A non-fungible token is a digital token - stored on a blockchain - that certifies a digital asset to be unique.
The best-known, and most expensive, NFTs have related to works of art.
The difference between an NFT and a cryptocurrency is that units of the cryptocurrency are fungible (interchangeable) and each of equal value.
NFTs are - by definition - unique and not interchangeable.
Accordingly, each NFT can have a different value.