In anatomy, the anus (from Latin ānus "ring, anus") is the external opening of the rectum. Closure is controlled by sphincter muscles Feces are expelled from the body through the anus during the act of defecation, which is the primary function of the anus. Most animals — from simple worms to elephants and humans — have a tubular  gut, with a mouth at one end and an anus at the other.

The American Nihilist Underground Society, or A.N.U.S., is an online organization known for spreading its interpretation of the philosophy of nihilism, and for its related website, the Dark Legions Archive (DLA), containing extensive coverage on heavy metal music with emphasis on extreme metal. The website also hosts the USENET-based Heavy Metal FAQ, and has a page titled "Altar of Unholy Blasphemy", which includes a close-up of a person's anus, with two hands opening it widely and showing an illustration of Jesus with a dollar sign on his forehead inside. The organization was started in the 1980s by several persons from River Oaks. On the Internet, it existed as bulletin board system postings in 1989. According to one of the organization's founders, Spinoza Ray Prozak (who formerly hosted a radio program titled "Oration of Disorder" on KSPC 88.7,), "A.N.U.S. organization exists to produce thought which will lead humanity to a better time".

“Anusim” (Hebrew: אנוסים), plural for anús, means forced ones in Hebrew. This is a legal terminology applied to a Jew who has been forced to abandon Judaism against his or her will, and who does whatever is in his or her power to continue practicing Judaism under the forced conditionoun It derives from the Talmudic term aberá be'ones [TB: Abodá Zará 54a], meaning "a forced transgression".