Sadism and masochism, in the sense, describe psychiatric disorders characterized by feelings of sexual pleasure or gratification when inflicting suffering or having it inflicted upon the self, respectively. Sadomasochism is used in psychiatry to describe either the co-occurrence of sadism and masochism in one person as separate disorders, or as a replacement for both terms, depending on the theory used. Definitions of sadism and masochism in medicine have been modified repeatedly since they were introduced by the Austrian psychiatrist Richard Freiherr von Krafft-Ebing in the 19th century (Krafft-Ebing 1901).