A "normal" lens (50mm) on a 35mm camera has a 46 degree field of view. As the focal range of the lens shortens, the field of view gets wider, thus "wide angle," indicating that the field of view, in degrees, has exceeded the focal length of the lens, in millimeters. (At least, that's the way it was explained to me...) At 35mm, the field of view has expanded to 64 degrees. At 28mm, it is 75 degrees. When you get down to the extreme wide-angle lenses, the field of view is tremendous. A 16mm lens, for example, would have a 115 degree field of view. Of course, this all changes with different types of camera. At 50mm, for example, an APS camera would have a 39 degree field of view, a 6x4.5 would have a 74 degree field of view, and a 6x6 would have an 81 degree field of view. Wide angle is basically a catchall term for any lens with a focal length of 50mm.
~Adam
(Source: Popular Photography/October 1997)