pronounced eff-sixty-five or eff-six-five, is an occasionally used term to describe a person who suffers from a paraphilia or disorder of sexual preference.

The expression derives from the International Classification of Diseases (ICD-10)of the WHO, wherein the mental and behavioural disorders (psychiatric conditions) are classified "F" and F65 refers to the disorders of sexual preference. The term is often used as a euphemism, and sometimes in a derogatory fashion.