A blockchain oracle is a service that brings outside information to a blockchain. Smart contracts can read blockchain data, but they usually need an oracle to use real-world facts such as prices or event outcomes.
Why oracles matter
DeFi lending, derivatives, insurance-like products, and automated settlement tools often depend on price feeds or external data. Without oracles, many smart contracts would not know what is happening outside their own network.
Oracle risk
If an oracle is wrong, delayed, manipulated, or too centralized, the smart contract using it may make bad decisions. Oracle design is therefore part of crypto security, not just a data feature.
Chainlink is one of the best-known projects associated with blockchain oracle infrastructure.