Paraphilia is any intense and persistent sexual arousal to atypical objects, situations, fantasies, behaviors, or individuals. Previously known as sexual perversion and sexual deviation, paraphilia is typically sexual interest other than the (sexual interest) in genital stimulation or similar or regular sexual activities with phenotypically normal, physically mature, consenting human partners.

Often, paraphilias are defined as recurrent, intense sexually arousing fantasies, sexual urges, or behaviors generally involving nonhuman objects, the suffering or humiliation of oneself or one’s partner, or children or other non-consenting persons.

This type of behavior includes a pattern of recurring sexually arousing mental imagery or behavior that involves unusual, and usually socially unacceptable sexual practices (e.g. sadism or pedophilia).

Origin of the word paraphilia is Greek. In Greek, 'para' means around or beside, and 'philia' means love.

Sexual behaviors that are considered as paraphilias are also treated by the societies as distasteful, unusual, or abnormal. One reason of that is such behaviors, sexual urges, or fantasies usually cause clinically significant distress and/or impairment in social, occupational, or other important areas of socio-cultural functioning.

These has been a debate over the number and taxonomy of paraphilia. According to Aggarwal (2008), there are as many as 549 types of paraphilia. Some of the most common types include:

• pedophilia: sexual interest towards children
• exhibitionism: exposure, or a desire for exposing an act of exposing genitalia to strangers or an unsuspecting person/people, or performing sexual acts in front of others
• voyeurism: observing private (sexual) activities of people without the victims' knowledge
• frotteurism: touching or rubbing someone without that person's consent

Also, the discussion of paraphilia often include or relate other behaviors that are sometimes considered as atypical, but not as sexual or psychological 'disorders' depending on some indices. These may include: fetishism (use of inanimate objects), sexual masochism (being humiliated or forced to suffer), sexual sadism (inflicting humiliation or suffering on another person), while transvestic disorder (sexually arousing cross-dressing) are much less common.

According to medical science, there is also a category of paraphilias known as 'Other Specified Paraphilic Disorders' that encompasses behaviors not covered by the already named diagnoses. This category includes sexual interests and behaviors including or involving corpses (necrophilia), urine, feces, enemas, or obscene phone calls.

According to medical science, paraphilias are almost exclusively diagnosed in men. Also, many people who have one paraphilia usually have more than one that is individuals displaying one paraphilia very often also exhibit other paraphilic behaviors.

Often being a medical concern, paraphilias are, in some cases, issues of legal concerns also.

What causes Paraphilia?

According to different medical resources including psychology experts, what causes paraphilia is not surely known. There are some differing theories about that. One school believes that issues like childhood trauma (e.g. sexual abuse) can cause it in the victim. Another school claims that a person's experience of objects or situations may be arousing if that is linked to a pleasurable sexual activity and develop paraphilic behavior in that person over time. According to Kafka (1997), the presence of paraphilic behavior in a person may represent an underlying sexual impulsivity disorder that is characterized by sexual compulsivity and hypersexuality, and in some cases - aggression.

Legendary Austrian neurologist and the founder of psychoanalysis Sigmund Freud believed that factors like troubling maladjustments in sexual development, and fixation of sexual aims or objects caused either by an actual trauma or the blockage of a powerful libidinal urge can also shape a person's sexual behavior.

Different perspectives

Also, we must consider the fact that there is a great deal of controversy concerning paraphilia: why and how it is developed in a person, and how to define them, when to identify such behavior as a disorder - how to draw the line between normal versus deviant or disordered -  given that this is, to some degree, dependent on cultural views of acceptability that varies from society to society, and from time to time.

And it is also important to acknowledge that there are multiple perspectives to look at into it: medical (clinical) point of view, psychological aspect, and socio-cultural perspective to mention some.

References
Aggrawal, Anil (2008). "Appendix 1". Forensic and Medico-legal Aspects of Sexual Crimes and Unusual Sexual Practices. Boca Raton, Florida: CRC Press. ISBN 978-1-4200-4308-2.
American Psychiatric Association (APA) Diagnostic and statistical manual of mental disorders DSM-IV-TR®. Washington DC: APA; 2000.
American Psychiatric Association (APA) Diagnostic and statistical manual of mental disorders DSM-5. Washington DC: APA; 2013.
Bhugra, D; Popelyuk, D & McMullen, I (2010). Paraphilias across cultures: contexts and controversies. J Sex Res. 2010. doi: 10.1080/00224491003699833.
Cantor, JM (2012). Is homosexuality a paraphilia? The evidence for and against. Arch Sex Behav. 2012;41:237–47. doi: 10.1007/s10508-012-9900-3.
Freud, Sigmund (1991). On Sexuality: Three Essays on the Theory of Sexuality and Other Works. Penguin Books, Limited. ISBN 978-0-14-013797-2.
Introduction to Sigmund Freud, Module on Psychosexual Development. Cla.purdue.edu. Archived from the original on 2012-12-11. Retrieved on 2020-07-22.
Kafka, M.P. (1997). Hypersexual Desire in Males: An Operational Definition and Clinical Implications for Males with Paraphilias and Paraphilia-Related Disorders. Arch Sex Behav 26, 505–526 (1997). [https://doi.org/10.1023/A:1024507922470]
Knight, RA (2010). Is a diagnostic category for paraphilic coercive disorder defensible? Arch Sex Behav. doi: 10.1007/s10508-009-9571-x.
Moser, C (2011). Yet another paraphilia definition fails. Arch Sex Behav. doi: 10.1007/s10508-010-9717-x.
Stuart, RS (2012). Constructing Perversions: The DSM and the classification of sexual paraphilias and disorders. Electronic J Hum Sex.
World Health Organization (WHO) ICD-10 Version:2010, Disorders of sexual preference. [http://apps.who.int/classifications/icd10/browse/2010/en#/F65]
Zonana, H (2011). Sexual disorders: new and expanded proposals for the DSM-5—do we need them? J Am Acad Psychiatry Law.
Zucker, KJ (2013). DSM-5: Call for Commentaries on Gender Dysphoria, Sexual Dysfunctions, and Paraphilic Disorders. Arch Sex Behav. 2013 doi: 10.1007/s10508-013-0148-3.

Dictionaries and other online resources:

britannica
disorders.org
emedicine.medscape.com
medicinenet.com
merriam-webster
wikipedia.org/wiki/Paraphilia