WTF is the Point of Equilibrium and how do you know what/where it is?

Everyone references this here and in T Tape videos but I have yet to see one single person explain anything about it. Typing it in the search bar just brings up people talking about it as if everyone already knows.

I assume it's not the scar line? How am I supposed to know where this is? Are there any videos or pictures or anything beyond just text descriptions?