A Non-fungible Token represents a unique digital item such as art pieces, songs, video shootings of any nature (movies, short clips), photographs, paintings, and even video games.
Also, Blockchain technology is what powers NFTs. Think of a blockchain as a ledger of registries they says:
Bruno is the author of this song
Alicia has recorded a version of Bruno’s original song
John has a copy of Alicia’s version of Bruno’s original song
.. and Blockchain is immutable. Therefore, if Bruno is the author of the song nobody can take that away from him.
Fungibility is an economics term that says that a good or commodity can be interchangeable between parts – it doesn’t happen in NFTs, but digital files, by themselves, can be reproducible millions of times. Also, the rights to reproduce a digital item such as a song or short movies can be assigned in the Blockchain and these rights can be certainly monetised.