Sexual intercourse (synonymously coitus or copulation) is the act of inserting the erect penis of the male into the vagina of the female, the primary step in sexual reproduction.

In a wider context, the term "sexual intercourse" may refer to any a wider range of sexual activities.

There is no clear borderline between sexual and nonsexual enjoyment of touching someone else's body. For example, holding hands may or may not have a sexual connotation, depending on culture, situation and other factors. There are, however, actions that are clearly sexual by almost anyone's definition but which have been argued by an accused as not having sexual relations since the most common form of heterosexual sexual intercourse had not occurred. The distinction between sexual and nonsexual behavior can be relevant due to social rules.