The Canon EF 50-200mm f/3.5-4.5 is an EF mount normal-to-telephoto zoom lens. It is one of the first lenses in the Canon EF series.
In June 1988, Canon announced the EF 50-200mm f/3.5-4.5L lens. This lens has very similar physical qualities compared to the EF50-200mm f/3.5-4.5. The main difference is that this is a L lens, which normally entails better environment sealing.
References
Canon EF 50-200mm lens Wikipedia(Text) CC BY-SA