Perversion is a concept describing those types of human behavior that are perceived to be a serious deviation from what is considered to be orthodox or normal. Although it can refer to varying forms of deviation, it is most often used to describe sexual behaviors that are seen as abnormal or excessive. Perversion differs from deviant behavior, since the latter refers to a recognized violation of social rules or norms (although the two terms can apply to the same thing). It is often considered derogatory and in psychological literature the term paraphilia is now used insteadMartins, Maria C.; co-author Ceccarelli, Paulo. The So-called "Deviant" Sexualities: perversion or right to difference? Presented in the 16th World Congress. "Sexuality and Human Development: From Discourse to Action." 10-14 March, 2003 Havana, Cuba., though this term is controversial.

The concept of perversion is subjectiveMartins, Maria C.; co-author Ceccarelli, Paulo. The So-called "Deviant" Sexualities: perversion or right to difference? Presented in the 16th World Congress. "Sexuality and Human Development: From Discourse to Action." 10-14 March, 2003 Havana, Cuba., and its application varies depending on culture. As a psychological term it was originally applied especially frequently to homosexual behavior.Online Etymological Dictionary: Pervert However, homosexuality is no longer treated as a disorder in mainstream psychiatry (see Homosexuality and psychology).

The verb pervert is less narrow in reference than the related nouns, and may be used with no sexual connotations.Dictionary.com: Pervert One might say, for example, that a modern film version of Romeo and Juliet "perverts" Shakespeare's version of the story.

The noun sometimes occurs in abbreviated slang form as "perv" and used as a verb meaning "to act like a pervert", and the adjective "pervy" also occurs. All are often, but not exclusively, used non-seriously.