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.