Buttocks can also be called a "butt". Another word for buttocks that some consider to be offensive is "ass".
The main function of buttocks is to help people sit. Buttock is also considered as an organ to arouse human sexuality. Buttocks are involved in anal sex. During anal sex, a male or female puts his penis or strap-on into the buttock's hole and moves it inward and outward. Sometimes a female or male inserts various sex toys into her or his anus for pleasure.