The InterPlanetary File System (IPFS) uses content-based addressing; the address changes every time the content does. For example, if you share an IPFS hash with someone, you will end up sharing a new link every time the content is updated.
The InterPlanetary Name System (IPNS) is a system for creating and updating mutable links to IPFS content. Even if you update the IPFS content, the IPNS hash will point to the latest version of that content. IPNS is not human-readable and the names are not assets on a blockchain.
A Web3 domain is an Ethereum/Polygon asset that relies on the security of the blockchain. You sign a message with your private key and associate your IPFS hash with your Web3 domain.