Blockchain oracle

A blockchain oracle is a third-party service for smart contracts. Oracles provide trusted information based on the outside-world sources to the on-blockchain smart contracts. An oracle typically encapsulates the real-world complexity outside of the blockchain, since the on-chain critical errors are hard to fix. For example, in a contract to automatically purchase bitcoins at a predetermined price, the fulfillment condition is based on the current exchange rate for the bitcoin; off-chain oracle constantly monitor the price to provide the triggering condition to the contract.