Chainlink is for solving the Oracle problem within the blockchain projects. Sometimes we need to rely on the outside data sources for smart contract executions, so how to use outside data in a reliable and standard way is quite important. Chainlink is an external data provider to blockchain projects. There are many cases that the trigger and execution of smart contracts rely on conditions of external data, like climate data. The key is that external data is reliable and tamper-proof. Chainlink manages to provide a standard, process, and APIs for easy use of external data.