Martin - did you ever get an answer? Buzzing is to play the mouthpiece alone, without the horn. See Robert Ward's post on "mouthpiece buzzing". There is also just buzzing your embouchure with no mouthpiece and no horn at all. Both can be useful exercises in small amounts. But you'll want a towel or napkin.
"Chops" means your lips, and I think all the muscles around your mouth, cheeks and chin. Embouchure I think refers to specifically the shape of your lips when in playing position, such as the difference between Ansetzen and Einsetzen (did I spell that right?) A person could have very strong, healthy chops but some wierd embouchure problems. Or a perfect embouchure but weak or worn out (or injured) chops.
