Sexual intercourse, in its biological sense, is the act in which the male reproductive organ (in humans and other higher animals) enters the female reproductive tract, called copulation or coitus in other reference. The two entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails.
Traditionally, intercourse has been viewed as the natural endpoint of all sexual contact between a man and a woman, and is commonly confined to this definition today. The meaning of the term, however, has been broadened in recent years, and now labels at least three different sex acts. These three types of intercourse are: vaginal intercourse, involving vaginal penetration by the penis; oral intercourse, involving oral caress of the sex organs (male or female); and anal intercourse, involving insertion of the male's penis into his partner's anus.
Sex acts that involve digital (use of fingers or hands) intercourse or mutual masturbation are more often referred to as outercourse (with oral sex at times listed as an aspect), while the term sex, in the context of sexual intimacy, is often understood more widely to include any mutual genital stimulation.
For most non-human animals, sexual intercourse is used only for reproduction[citation needed, through insemination and subsequent internal fertilization. However, bonobos, dolphins and chimpanzees are known to engage in sexual intercourse even when the female is not in estrus, the most fertile period of time in the female's reproductive cycle, and to engage in sex acts with same-sex partners. In most instances, humans have sex primarily for pleasure. This behavior in the above mentioned animals is also presumed to be for pleasure, which in turn strengthens social bonds.

An orgasm (sexual climax) is the conclusion of the plateau phase of the sexual response cycle, and may be experienced by both males and females. Orgasm is characterized by intense physical pleasure, controlled by the involuntary, or autonomic, nervous system. It is accompanied by quick cycles of muscle contraction in the lower pelvic muscles, which surround the primary sexual organs and the anus. Orgasms are often associated with other involuntary actions, including muscular spasms in other areas of the body, a general euphoric sensation, and frequently, vocalizations. After orgasm, humans often feel tired and a need to rest. This is attributed to the release of prolactin. Prolactin is a typical neuroendocrine response in depressed mood and irritation. Ongoing research at the University Medical Center of Groningen, the Netherlands, studies brain events that accompany orgasm in men and women. Techniques used involve Positron Emission Tomography (PET) and fMRI. Male and female brains act almost the same during orgasm. Brain scans showed that large parts of the cerebral cortex temporarily reduced their activity.

Human sexual behavior or different human sexual practices encompass a wide range of activities such as strategies to find or attract partners (mating and display behaviour), interactions between individuals, physical or emotional intimacy, and sexual contact. Some cultures will find only sexual contact within marriage acceptable; however, extramarital sexual activity still takes place. Unprotected sex may result in unwanted pregnancy or sexually transmitted diseases. In some areas, sexual abuse of individuals is prohibited by law and considered against the norms of society.