Off-Chain Data
Information about digital assets that does not live on a blockchain, such as exchange trades, company disclosures, and price feeds.
Much of what matters happens off-chain: centralized exchange order books and trade prints, custodian and fund reports, regulatory filings, over-the-counter desks, and development or social activity. It is indispensable because a large share of trading, and most institutional activity, never touches a chain, and because price itself is an off-chain observation. Its weaknesses are the mirror image of on-chain data: it is self-reported, revisable, unevenly covered across venues, and there is no consolidated tape of the kind regulated equity markets maintain. Oracles are the mechanism by which selected off-chain values, usually prices, are brought on-chain for contracts to use.
En pratique
A lending protocol liquidating a position relies on a price that originated off-chain and was delivered to the contract by an oracle.
Le malentendu courant
Off-chain does not mean unimportant or unverifiable; exchange trading is off-chain, and the price used in nearly every on-chain metric starts there.