Try   HackMD

What is Chainlink ?

ChainLink is the leading decentralised oracle solution. It bridges off-chain data to on-chain data.

It is used whenever a smart contract need accurate real world data to work, can be prices, weather, sport results

For example : ChainLink price feeds are used by many DeFi app that need aggregated price of a token.

You can learn more about ChainLink on their official website.