What does TEE (Trusted Execution Environment) mean?

A hardware-isolated region of a CPU (an "enclave") whose memory and execution are shielded from the operating system, the hypervisor, and even the machine's owner.

It can also produce a signed attestation proving a specific unmodified program ran inside and produced a given output. Oracles use a TEE so the data they feed on-chain carries hardware-backed evidence it was fetched faithfully.