Waves: Data Oracle Tool
A smart contract written on the blockchain is unable to access data outside its own network. This problem is resolved by using data oracles, which are basically agents that find real-world information and feed it to the blockchain for use by smart contracts and dApps.
In other words, oracles are tools that facilitate communication between the blockchain and the real world. Data they feed to the blockchain could be as diverse as currency exchange rates, weather reports, results of elections or sporting events, commodity prices or even flight and train timetables.