What ChainLink use for?

The data that ChainLink can integrate with are vast due to many business partners. It could be Bank transaction from VISA card, Paypal, Accounting data from SAP, Salesforce, Stock exchange data from New York (NYSE), Economic data from Bloomberg, other data from other Blockchain, HyperLedger, and even GPS or weather data from satellite

The example of its application is the use of security smart contact that require API to report an index in stock exchange like Derivatives : Future trading or Stock option that limited gain or lost automatically by smart contract or purchasing of Bonds & investment unit that require to pay interest which will also paid by smart contract.