TEE is the acronym that is used for Trusted-Execution-Environment.
A Trusted Execution Environment is a highly secured area for the processing of data which guarantees performance that preserves the integrity of the input code & output data. TEE’s can be both hardware devices that are provably un-compromised and universally recognized as trust-worthy, as well as, software (primarily OS level stuff such as the Kernel.
The use of TEE’s in the cryptocurrency and blockchain industry is that of created complete end-to-end trust solutions.
An application that is downloaded from an app store is NOT a TEE; while the MACOS kernel that does time-keeping is.