Smart contracts are deterministic and cannot natively access off-chain data. Oracles bridge this gap by delivering external information — like asset prices — on-chain. The most widely used pattern is a push oracle, where a decentralized network periodically writes prices into an on-chain contract that other contracts read.

Chainlink's price feeds are a canonical example. Each feed stores a value with metadata:

roundId — monotonically increasing identifier for each update
answer — the price, scaled by a fixed number of decimals
updatedAt — Unix timestamp of the last write
answeredInRound — guards against stale round data

Feed	Decimals	Heartbeat
ETH / USD	8	~1 hour
BTC / USD	8	~1 hour
USDC / USD	8	~24 hours

Consumers must always validate staleness (updatedAt within tolerance) and completeness (answer > 0, answeredInRound ≥ roundId) before acting on a price.