Jack Dorsey is selling his first tweet as an NFT.

NFT stands for Non Fungible Token. They are digital assets than run on blockchain technology the same way cryptocurrencies do. NFTs are not exchangeable the way money (or currency is). Instead they should be regarded the way you might rare art or baseball cards.
The tweet from 2006 reads “Just setting up my twttr.”
The winning bidder will receive a digital certificate of authenticity signed by Dorsey, and the tweet’s metadata. The current high bid is $2.5 million.