Decentralized applications, or dApps, are applications that are built on top of a blockchain or peer-to-peer network, commonly using Ethereum.
You can think of a decentralized application as an app that is not controlled by one entity but by a network of people working together. Anyone can help improve the app and nobody can make a change without everyone agreeing. Tokens are often used to represent ownership, distributed through a predefined algorithm, for those who are contributing/developing, fundraising or in some cases mining.
Twitter and Netflix are examples of centralised applications whilst CryptoKitties is an example of a decentralized application. We are already seeing dApps being used in industries such as energy, health, social, education, finance, insurance, property, gambling, games… the list goes on and on.
A brilliant visual explanation of dApps by Whiteboard Crypto.
What blockchain are dApps commonly built on?