An NFT, or Non-Fungible Token is basically just a box that a bit of code can go into. It's too small to save anything of any actual size, and correcting bugs in code is expensive and difficult, so the incentive is to just use the token as a link to some external site.

NFT avatars are the result. An image is procedurally generated and saved on some server. The "buyer" pays an exorbitant sum to "own" the image, but has no special rights over it. The token is uniquely owned, the image it links to is infinitely reproducible.

Cryptobros insist this is an investment, because someone will definitely want to buy the token someday. Everyone else finds the idea laughable and the enthusiasts obnoxious.