Frotteurism refers to a paraphilic interest in rubbing, usually one's pelvis or erect penis, against a non-consenting person for sexual gratification. It may involve touching any part of the body including the genital area. A person who practices frotteurism is known as a frotteur. The majority of frotteurs are male and the majority of victims are female, although female on male, female on female, and male on male frotteurs exist. This activity is often done in circumstances where the victim cannot easily respond, in a public place such as a crowded train or concert.
Usually, such nonconsensual sexual contact is viewed as a criminal offense: a form of sexual assault albeit often classified as a misdemeanor with minor legal penalties. Conviction may result in a sentence or psychiatric treatment.
The term frotteurism derives from the French verb frotter meaning "to rub". The term frotteur is the French noun literally meaning "rubber" or "one who rubs" and was coined by sexologist Richard von Krafft-Ebing in his book Psychopathia sexualis (1886). 
The psychiatric handbook, the DSM (see below), used to call this sexual disorder by the name frottage until the second edition (DSM II). However, this term is no longer used in the United States to refer to the sexual disorder, which is now called frotteurism, as it is in the current fourth edition (DSM IV). Nevertheless, the term frottage still remains in some law codes where it is synonymous with the term frotteurism. "Frottage" is now used for consensual rubbing (a.k.a., "dry humping") as part of normal sexual activity.
The professional handbook of the American Psychiatric Association (APA), the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, text revision (DSM IV-TR), lists the following diagnostic criteria for frotteurism.
- Over a period of at least 6 months, recurrent, intense, or arousing sexual urges or fantasies, that involve touching and rubbing against a nonconsenting person.
- The person has acted on these sexual urges or fantasies, or they cause the person significant distress, to a degree they are disruptive to everyday functioning.
DSM IV classification 
According to DSM IV (Diagnostic and Statistical Manual, IV edition), where all psychiatric illnesses are represented as numerals to avoid confusion, frotteurism is classified as 302.89.
See also 
- Courtship disorder
- Eve teasing
- Kazuhide Uekusa
- Chaim Halpern
- Non-penetrative sex
- Sexual harassment