I'm often confused because "decentralized" means different things to different people, like the fable of the blind men and the elephant.
BitTorrent and other peer to peer apps are decentralized, but are they really when the data flows through the pipes of a few Telco's?
I think web3 means there isn't a central authority for conducting transactions with other people, but I have a nagging feeling that this could be accomplished without a blockchain and proof of work waste.