There are bull's head, dog's head, spittoon's head and other heads in the lens. What heads do these refer to?

Tauren is expensive, and good shots are basically divided into tauren. The ferrule is a lens sold with the SLR body. Of course, it is also sold separately. Dog's head is the antonym of cow's head, and it is also often used to describe the head. The spittoon head is a Canon lens, adjective 50 1.8. The price of less than one thousand yuan can compete with the zoom of ten thousand yuan.