A 1999 study by the Kinsey Institute examined the definition of sex based on a 1991 random sample of 599 college students from 29 U. states; it reported that while "virtually every college student they surveyed considered penile–vaginal intercourse to be sex," and 19–20% said that anal intercourse was not sex, 60% said oral-genital contact (fellatio, cunnilingus) did not constitute having sex.
Various jurisdictions have placed restrictive laws against certain sexual acts, such as incest, sexual activity with minors, prostitution, rape, zoophilia, sodomy, premarital and extramarital sex.
Reproductive sexual intercourse between non-human animals is more often termed copulation, and sperm may be introduced into the female's reproductive tract in non-vaginal ways among the animals, such as by cloacal copulation.
For most non-human mammals, mating and copulation occur at the point of estrus (the most fertile period of time in the female's reproductive cycle), which increases the chances of successful impregnation.
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.
Religious views on sexuality vary significantly between different religions and sects of the same religion, though there are common themes, such as prohibition of adultery.