The EF 50mm lenses are a group of normal prime lenses made by Canon that share the same focal length. These lenses are based on the classic double-Gauss lens, with the f/1.8 being a standard six-element double-Gauss with an air gap and powers between element 2 and 3 and its faster cousins adding additional elements.
The 50mm focal length, when used with a 35mm film or full-frame sensor, has been widely considered to match the perspective seen by the human eye.
Canon 50mm lenses have an EF type mount that fits the Canon EOS line of cameras. When pairing a 50mm lens to a Canon DSLR with an APS-C sized sensor, the crop factor effectively turns the 50mm focal length into an 80mm field of view.