I believe Greg talked about Sympathetic vs Synthetic Oscillation early on in the course.
He touches on it in “Largo Fundamentals – The Leadpipe SHAPE Revisited” and these videos:
The concept, in a nutshell, is that we don’t buzz the lips to produce sound on the Trumpet. We can, but the sound will be tight and nasally, especially in the lower register. The lips actually sympathetically vibrate when the sound wave in the trumpet vibrates.
The concept is that we want to be as efficient as possible, as that will enable us to have the best sound and the highest possible range.