A dApp (decentralised application) typically looks like an ordinary website or app, but instead of talking to a private company's backend servers, its core logic runs on smart contracts deployed on a public blockchain. The front end you see in your browser is just an interface to that on-chain logic.
This distinction matters for security: a convincing-looking front end can still connect to a malicious or fake contract, so verifying you're interacting with the genuine, audited contract behind a dApp is a real and important step, not a formality.