A wide angle lens is essentially the opposite of the Telephoto lens. Telephoto lenses work by increasing the focal length (the distance between the front of the lens and the film) to capture objects far away. Wide angle lenses work by decreasing the focal length and bringing the lenses closer to the film.
An extreme example of a wide angle lens is the ‘fisheye’ lens.
An image taken with a fisheye lens. Credit: ESO/José Francisco Salgado (josefrancisco.org) CC By 4.0
Wide angle lenses are great for photographing landscapes and architecture, and can also be used for some fun effects.