A Trusted Execution Environment (TEE) is a secure area within a main processor that ensures sensitive data is processed in a protected environment. It creates a barrier against unauthorized access, allowing applications to run securely even if the main operating system is compromised. TEEs are commonly used in devices like smartphones and tablets to safeguard personal information and transactions. TEEs utilize hardware-based security features to isolate and protect code and data. This means that applications running in a TEE can trust that their operations are secure from external threats. Technologies like Intel's SGX and ARM's TrustZone are examples of how TEEs are implemented in modern computing systems.