chastity belt
A type of groin covering that shields its wearer against sexual contact. Usually locked in place and intended for long-term wear. In historical times these were indeed used to ensure chastity (of princesses and such), but nowadays they survive within the BDSM subculture as a method of erotic sexual denial.
Modern chastity belts are manufactured in both male and female varieties, and some allow for performing bodily functions without needing to remove the belt.
Not to be confused with a chastity cage, which serves a similar purpose, but wraps around the wearer's penis only, instead of their entire waist.