Blockchain oracles connect blockchains to external events, which allow smart contracts to execute based on events happening off-chain. While oracles themselves are not data sources, they conduct the processes to gather, verify, and relay off-chain information to smart contracts and blockchain platforms.

https://cointelegraph.com/learn/what-is-a-blockchain-oracle-and-how-does-it-work

https://www.coinbase.com/learn/crypto-glossary/what-is-a-blockchain-oracle-in-crypto

https://chain.link/education/blockchain-oracles

https://worldcoin.org/articles/what-is-an-oracle-in-blockchain