Perversion is a term an 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 instead, though this term is controversial.