The opening in the rectum, where fecal matter is expelled from, and a sexual zone for many.
Located between the butt cheeks, this is the spot where one defecates from, but is also a primary erogenous zone for both women and men.
In homosexual sex, the anus is a primary source of sexual pleasure, as well as a high risk for potential health risks, such as the transmission of sexually based diseases.
This includes the transfer of the HIV virus, but also includes risk to tearing of the internal lining of the rectal area.
From Latin 'anus' meaning circle, ring.
The anus is considered a high risk area of the body, subject to various diseases, most notably Cancer.
History (Legend): Originally, the term 'anus' was considered to be vulgar, due to its function, and in polite circles was referred to as 'fundament' which has since mainly disappeared from society, as 'anus' has become more acceptable in all social circles.
Due to the high concentration of various nerve endings around the anus, and within, it is a popular orifice for sexual stimulation, either through direct penis penetration, or other devices.
For many receiving some form of anal penetration, it is believed to be due to the prostrate gland located within, as well as the high concentration of nerve endings.
For those doing the penetration, with their penis or finger, it is the tightness that they feel, that accentuates the pleasure feelings.
Practice (Associated Acts): Sexually, the insertion of any inanimate object can be pleasurable to the receiving person (male or female). Care has to be taken, to avoid tearing of the lining, as well as in introducing germs and disease directly into one's body, thus proper sterilization of all inanimate objects being used should be practices.
Use of condoms on such 'devices' should be practiced, including when one uses their penis for penetration.
Noteworthy: Freud in his theory of psychological development had a stage called the 'anal stage' in which he believed that toddlers derived pleasure from the act of having bowel movements. It led to the term 'anal' and the more derogatory term 'anal retentive'.
In many cultures, anal sex is considered Taboo, and has been referred to as 'sodomy' 'buggery' which carry criminal penalties. Only recently has such laws, such as in Texas, been over turned.
There are still many areas where such laws carry stiff penalties, such as in Iran and other restrictive societies.