According to Wikipedia, Superdrol is the brand name for a brand of methasterone. Superdrol is an anabolic steroid that is marketed as a "designer" steroid rather than being used for medical purposes. Steroid.com explains that it is a cutting steroid, preserving lean tissue during dieting.
Because methasterone was not commercially available when the U.S. Anabolic Steroids Control Act of 1990 was signed into law, it is not declared a Schedule III class anabolic steroid. It can therefore be sold as an over-the-counter dietary supplement. Its use has been prohibited by the World Anti-Doping Agency. Despite this, and despite a U.S. Food and Drug Administration warning against methasterone, Superdrol is available as a supplement, as of 2014.