Chainlink (LINK) is an ERC-20 token designed/based on the Ethereum blockchain. The token serves as a payment for Chainlink Node operators for their off-chain data retrieval, formatting data into blockchain readable formats, off-chain computation and uptime guarantees.
The token also functions as collateral for node operators to prevent bad actors. Its network provides a bridge between cryptocurrency smart contracts and off-chain resources (e.g. data feeds), various web APIs and traditional bank account payments. Chainlink allows smart contracts to communicate with external resources on its own. It is considered a middleware meant to serve as an oracle that links smart contract with real world data. More precisely, a series of decentralized oracles link with blockchain APIs.