What does poison head mean?

In photography, it refers to the lens at the top.

In photography terminology, "poison head" refers to those top-level lenses that are expensive and have perfect imaging quality. These lenses are sought after by professional photographers and can provide excellent image quality and excellent performance. This title stems from its addiction, fascination and yearning, just like "drugs". Having a "poisonous head" is considered to be the dream of photographers or professional photographers.