The Ethereum Org frames the difference between Web2 and Web3 as follows:
Web2 refers to the version of the internet most of us know today. An internet dominated by companies that provide services in exchange for your personal data. Web3, in the context of Ethereum, refer to decentralized apps that run on the blockchain. These are apps that allow anyone to participate without monetising their personal data. – WEB2 vs WEB3
On the other hand, back when Ol' Pmarca had a blog, he penned an essay in which he claimed that "There's no such thing as Web 2.0". To give him his due, he was making a slightly deeper point that Web 2.0 really a set of design patterns that Web services/companies used and that there was really no difference between Web 1.0 and Web 2.0.
Looking back at the way the internet has evolved, I do think the Web1, Web2, and Web3 model/nomenclature actually has some purchase. However, rather than framing this as a set of design patterns of the companies, I think about it just as rough mile markers for the cultural zeitgeist and what that portends for the future of technology.
- Web1 – 1994 Netscape IPO: Signaled the beginning of the shift from the AOL walled garden to the open internet.
- Web2 – 2004 Google IPO: Signaled the coming hegemony of the paid advertising business model which was ultimately coronated with the FB IPO in 2012.
- Web3 – 2021 Coinbase IPO: Signaled that decentralization is the next big wave in computing.