

its from terry davis, the schizophrenic talented developer who wrote his own OS (TempleOS) from scratch as one of gods temples or something, however he was pretty racist and delusional, so would see “glowies” of CIA agents or whatever trying to get him, and now the term is used for people suspecting others of being federal agents
generally, it separates core functions of your phone from google, and lets you decide how much data to share with google via permissions (can be none, can be like stock android), just like any other app.
they also put lots of work into hardening the os against attacks such as the ones used by police and spyware companies to unlock phones, and are basically the only phone configuration consistently safe against those companies.
the day to day experience is pretty much the same as stock android, as long as you install google services. main issues with it (I have heard, I haven’t ran into these on my install) are some banking apps, and google pay doesn’t work.