Swarm is a censorship resistant, permissionless, decentralised storage and communication infrastructure.
This base-layer infrastructure provides these services by contributing resources to each other. These contributions are accurately accounted for on a peer to peer basis, allowing nodes to trade resource for resource, but offering monetary compensation to nodes consuming less than they serve.
From the end user’s perspective, Swarm is not that different from the world wide web. In the background, the difference is that content is hosted on a peer-to-peer storage network instead of individual servers. This peer-to-peer network is self-sustaining due to a built-in incentive system which uses peer-to-peer accounting and allows trading resources for payment. Swarm is designed to deeply integrate with the devp2p multiprotocol network layer of Ethereum as well as with the Ethereum blockchain for domain name resolution, service payments and content availability insurance.
About section based on the official Swarm website.