Chainlink is the industry-standard decentralized oracle network that solves the "oracle problem" by connecting smart contracts with real-world data. Blockchains cannot access external information on their own, so Chainlink acts as a secure bridge, enabling smart contracts to react to real-world events using verified, tamper-proof data. It is widely considered one of the first decentralized oracle networks and is the market leader in bringing off-chain data on-chain.