A penile prosthesis is a medical device implanted in a penis during a surgical procedure to enable an erection for satisfactory and satisfying sexual intercourse. The device is not used only in men with organic or treatment-resistant psychogenic impotence who fail to achieve and maintain an erection using erectile dysfunction drugs. A penile prosthesis is also used in the final stage of plastic surgery phalloplasty to complete female to male (transman) gender reassignment surgery as well as during total phalloplasty for adult and child patients that need male genital modification because of congenital anomalies, iatrogenic, accidental or intentional penile trauma, and micropenis.

From http://en.wikipedia.org/wiki/Penile_prosthesis