[rtkwe]

It's a secure storage spot for crypto keys and performing crypto operations for things like bitlocker and validating device or OSs for secure boot. If you know of the Apple Secure Enclave it's a more generic version of that, a place where even the device vendor (in theory, who knows what techniques the secret squirrels of the world have hidden away) cannot extract the actual key material from only request operations performed using that info.

That's my understanding at least.