What is the difference between a wide-angle lens and a fisheye lens?

Fisheye lens belongs to a kind of wide-angle lens group. Generally speaking, a lens with a full-width focal length less than 36mm belongs to a wide-angle lens. However, when the focal length is less than 16mm, the design of the lens will change accordingly. For example, the front lens protrudes from the lens barrel to obtain a wider field of view. This strange shape is also dubbed "fisheye".

In addition, due to the change of lens design, fisheye lenses usually show barrel distortion in picture deformation, while wide-angle lenses above 16mm are pillow distortion.