A decentralised application, often shortened to dapp, is an application built on a decentralised network. Ethereum describes a dapp as combining a smart contract with a frontend interface.
The parts of a dapp
On Ethereum, the smart contract is code on the blockchain. The frontend is the interface a person uses. Ethereum notes that a dapp can use ordinary frontend languages, and that a frontend may be hosted through decentralised storage.
The word “may” matters. A dapp’s frontend hosting is a design choice, not a universal requirement. The decentralised part may be the application backend, while other components can work differently.
Decentralisation can vary
Ethereum documentation cautions that a dapp can retain centralised elements, such as a centrally served frontend, server-side key storage or important off-chain business logic. For that reason, “dapp” should not be treated as an all-or-nothing label.
What the label does not guarantee
Calling an application a dapp does not by itself show that every part is decentralised, that it has no operator, or that it is secure, independent, accessible or suitable for a particular purpose.
Source
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