What's the difference between wide angle and focal length?

Wide-angle focal length is a classification that describes the focal length of camera lens. The lens of a camera can be divided into wide-angle focal length, standard focal length and telephoto focal length. Its classification standard is that the length of the focal length is approximately equal to the diagonal length of the display (the picture of the film machine). Using a camera with a picture size of 24mm×36mm, the standard focal length is about 45-55 mm ... A lens shorter than the standard focal length becomes a wide-angle lens, and a lens longer than the standard focal length becomes a long-focus lens or telescope head. At present, the wide-angle focal length of digital cameras is generally18-28 mm.