It is a sexual perversion, it occurs when someone gets excited causing the suffering or humiliation of others; by extension is any pleasure in witnessing or causing harm. The name comes from the French writer Donatien Alphonse Francois, Marquis de Sade, who was imprisoned for 27 years for sexual offences, at which time he wrote his works with accounts of torture, rape and crimes, all justified by false reasoning and sofismas, but with very revealing descriptions of his paraphilia.
