A Trusted Execution Environment (TEE) is a secure area within a processor that runs code in isolation from the rest of the system, ensuring that the data and operations inside it cannot be tampered with or observed by external software, even the operating system. In blockchain, TEEs are used for secure key management, confidential smart contract execution, and private transaction processing. Projects like Secret Network and Oasis Network leverage TEEs to enable privacy-preserving computations on public blockchains.