Perversion is a term and 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 decsribe 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 instead, though this term is controversial.
The concept of perversion is somewhat subjective, and its application varies depending on culture. As a psychological term it was originally applied especially frequently to homosexual behavior. However, homosexuality is no longer treated as a disorder in mainstream psychiatry.