From The Art and Popular Culture Encyclopedia
Anal sex or anal intercourse is a form of human sexual behavior. While there are many sexual acts involving the anus, anal cavity, sphincter valve and/or rectum, the term "anal sex" is often used to mean the insertion of the penis into the rectum. It is a form of sexual intercourse considered to be particularly risky, for a number of reasons related to the vulnerability of the tissues and the septic nature of the anus.
Such relations have been documented in a wide range of cultures, from earliest times. Where they involved two males, they have also been controversial and sometimes condemned since antiquity. Anal sex is encountered among people of all sexual identities and orientations. While it is reported more frequently among male couples, in absolute numbers more heterosexual couples have anal sex.