dApps are “decentralized applications.” This means that the app’s core functionality isn’t run on a company server but on a decentralized ledger like Ethereum. You might access a dApp through a mobile app or a webpage, but the smart contract core of the dApp ensures that the app does not rely on a third party to continue to operate or be trusted to do the right thing.
A traditional application like Facebook or TikTok lives on a server controlled by the company, giving the company full control over who can access the app or how it's used by the company.
dApps are decentralized, meaning they don't rely on a single entity. Instead, they run on the combined computing power of a decentralized public ledger. Some of the better-known dApps include CryptoKitties, Aave, and SushiSwap.
On Radix, a dApp has been specifically defined. See the Radix Tech Docs for more details on dApp definition.