It's a series of observations of general patterns of how brass playing works, broken down into several different pathways (different embouchure types and tongue types) and how each works...
Its worth mentioning that the term "pivot" can be a bit misleading - it's not what youd think (change of angle about a fixed point), it's more of a slide but that's a very simplified version.
As a word of warning... it can be a case of a little information being very dangerous. It's interesting to know about, but attempting to self-diagnose anything can be very unwise: don't go there - if you want to learn about how you play and what the best way to proceed is, you'll want a teacher who knows it inside out.
There are some videos on YouTube by a user called "wilktone" which introduce the basics in a kind of stripped down and more easily digested form, which you might find interesting.
Oh well.....thanks for explaining Tom-King. I'll continue my quest for embouchure perfection in my sound studio ( the spare bedroom). Currently making notes (written) on the outcomes of where my gob is in relation to mouthpiece when I play a 'nice' sound. And also when I play 'nasty' sounds.
Maybe a bit old school....but there you go.