Oracles
An oracle is a service that brings real-world data — like prices or weather — onto the blockchain for smart contracts to use.
In depth
Blockchains are sealed systems; a contract cannot fetch a stock price on its own. Oracles publish that data on-chain, ideally by aggregating many sources so no single feed can be manipulated. Lending protocols, derivatives and stablecoins all depend on oracle price feeds.
Why it matters
Bad oracle data has caused some of DeFi’s largest losses; it is a key risk to understand.