NFT stands for non-fungible-token. This means that the token is unique and not interchangeable with any other NFT, whether from the same series or another.
Imagine trading 100 NXRA with someone. It does not make a difference which NXRA tokens you are holding. However, with NFTs, all are numbered differently and contain a unique image, gif, video, song, etc. The proof of ownership of the NFT is stored on the blockchain.
Find out more about NFTs on Investopedia.