A variant of the wide angle lenses is called Fisheye lens and provides a viewing angle of up to 180 degrees. The name Fishey comes from the yeah, you guessed right - the fish's eye, and this is because the Fisheye lens is a lens which, like the fish eye, is arched.
It is an extreme wide angle lens, the most extreme ones out there. Situations where the Fisheye lens is often present is action and sports photography. Perhaps you have seen photographs taken dangerously close skateboarder or images taken from inside a ice hockey goal or behind the goal in soccer? If yes, then chances are that they are taken with a fisheye lens. As the picture becomes arched and with a 'barrel look' it often requires special software or some time in an image editing program to 'straighten out' the picture and its some what distorted appearance unless that effect is desired.
Worth thinking about is that Fisheye lenses rarely can have filters because they have a convex lens at the front (the front lens).
Five exemples of Wide Angle Lenses with Fisheye-character (see all)