Web3 is shorthand for the next iteration of the world wide web, which is based on blockchain technology. Web 1.0 refers to the web’s early days, when most sites consisted of static pages and the majority of web users consumed web content rather than produced it. In Web 2.0, the web became a platform on which users could create content and engage with other users using forums, social media and networking services, blogs, and wikis. That is the version of the web that most of us use today.
But Web 3.0 (or web3) envisions a fully distributed web based on blockchain technology like distributed ledger storage, tokens and NFTs. Unlike Web 2.0 where data and content (and, some say, power) are concentrated in the hands of a few giant tech companies, web3 will see people owning their own content and able to interact directly with one another, without needing a company in the middle to facilitate that transaction.
You can learn more about web3 here.