A fisheye lens is a wide-angle lens that takes in a broad, panoramic and hemispherical image
"In photography, a fisheye lens is a wide-angle lens that takes in a broad, panoramic and hemispherical image. Originally developed for use in meteorology to study cloud formation and called "whole-sky lenses", fisheye lenses quickly became popular in general photography for their unique, distorted appearance. They are often used by photographers shooting broad landscapes to suggest the curve of the Earth. Hemispherical photography is used for various scientific purposes to study plant canopy geometry and to calculate near-ground solar radiation."
It is most famously used in Missy Elliot videos, in the R'n'B and Hip-Hop/Rap genre. A reason Missy Elliot might use FishEye Lens is because she isn't the stereotypical slim, good looking, glamorous female, she dresses in baggy unflattering clothes and uses this type of lense to not show her body in the shot.
Also other people such as Busta Rhymes uses the fish eye lense for a different effect and to make them look intimidating.