Web1: run a server, people (clients) post content, and you save it on your server. Web2: pay someone else to run a server "in the cloud". They save the content

Web1: run a server, people (clients) post content, and you save it on your server. Web2: pay someone else to run a server "in the cloud". They save the content. Web3: run a server with all your own content. Other people run clients that index and let you search other peoples' content. Concisely: Web3 is the same as Web1, but with client-server the other way around.