Perversion is a derogatory term for deviation from the original meaning or doctrine, literally 'turning aside' from what is perceived to be orthodox or normal. A pervert is a person in a state of perversion. By apocopation a 'pervert' becomes a 'perv'. These terms have two common usages:

• It often refers to "sexual perversion", more neutrally called a paraphilia with some labelled as sex crimes.

• The term perversion was also used in the pre-Vatican II era by some Roman Catholics to describe the process of converting from Roman Catholicism to Protestantism. Whereas a protestant who joined Roman Catholicism was described as a convert, a Catholic who became a Protestant was called a pervert. The phrase is no longer used by mainstream Catholicism, though a small conservative fringe do on occasion still use it.

The verb form of the term, in general usage, simply means to turn something away from its natural state (or what is perceived to be its natural state.) For example, one might say that the modern film version of "Romeo & Juliet" perverted the story.