It’s the blanket name for their security architecture. The thing that makes sure your kernel is blessed, tries teo tell if you’re rooted, then sets a fuse flag if anything is off. It also provides a secure, encrypted profile for your phone that bifurcates apps, data, blocks screenshots. The data from the flag is available to apps to tell that your phone is potentially insecure. For the most part, they only block Samsung banking/pay apps and make your secure partition inaccessible.

My next phone will be something degoogled. hopefully something linux.

I’ve already wiped an old disconnected android phone for use with my drone/cameras that require a mobile device.