Sadism is defined as the deriving of sexual gratification from inflicting pain or emotional abuse on others.
The term sadism is derived specifically from Sade, Marquis de (Comte Donatien Alphonse Francois) (1740-1814), a French soldier and writer. From the time that he was a young nobleman Sade consorted with prostitutes and developed a taste for sexual perversions.
Within the BDSM community, the Dominant is most often the sadist, and the submissive is generally the masochist (who derives pleasure from receiving pain). In the BDSM community, sadism is widely accepted as a healthy expression of inflicting pain in a safe, sane, and consensual manner to a masochist who seeks such activities as a form of emotional release or sexual pleasure.
Masochism is the counterpart to sadism, the sexual pleasure or gratification of having pain or suffering inflicted upon the self, often consisting of sexual fantasies or urges for being beaten, humiliated, bound, tortured, or otherwise made to suffer, either as an enhancement to or a substitute for sexual pleasure.
The name is derived from the name of the 19th century author Leopold von Sacher-Masoch, known for his novel "Venus in Furs" that dealt with highly masochistic themes.
A masochist generally does not take pleasure in any arbitrary form of pain, only in pain received under the pretext of enforcing authority, and typically only that of a sexual nature. Likewise, a sadist usually only takes pleasure in pain that is inflicted for reasons of punishment and control, and most often for the indirect pleasure of the masochist. Many sadomasochistic activities involve only mild pain or discomfort. Often they are focused primarily on roleplay.
The term BDSM has been created to describe the quite common activities between consenting adults that contain sadistic and masochistic elements. Activities such as erotic spanking and love-bites that many people think of only as "rough sex" also contain elements of sado-masochism.