Vaginal intercourse also referred to as sexual intercourse involves inserting the penis into the vagina. Buehrens and Forrest Church. Anal sex involves stimulation of the anus , anal cavity, sphincter valve or rectum ; it most commonly means the insertion of a man's penis into another person's rectum, but may also mean the use of sex toys or fingers to penetrate the anus, or oral sex on the anus anilingus , or pegging. American Pregnancy Association. Religious beliefs also play a role in personal decisions about sexual intercourse or other sexual activity, such as decisions about virginity ,   or legal and public policy matters. There are 19 million new cases of sexually transmitted infections every year in the U.