The term used to describe someone who is addicted to pain is "masochist." A masochist is someone who derives pleasure or gratification from experiencing physical or emotional pain or humiliation. This term is derived from the name of the Austrian writer Leopold von Sacher-Masoch, who explored themes of masochism in his literary works. It's essential to note that masochism, like any other form of addiction or behavior, can be a complex psychological phenomenon, and seeking professional help is crucial for individuals struggling with such tendencies.