What is an NFT?

A Non-fungible token (NFT) is a unique and non-interchangeable unit of data stored on a blockchain, a form of digital. NFTs can be associated with reproducible digital files such as photos, videos, and audio. - Wikipedia

Fungible items can be replaced by another identical item; mutually interchangeable. (Example: gold)

Non-fungible items are unique digital identifiers that can not be copied, substituted, or subdivided and it is recorded by block chain.

Token - voucher that can be exchanged.

Basically it is a digital token (coin, image, audio file, or video) that is tracked by a block chain.