a touch or caress of the lips upon the lips, cheek, hand, or feet of another to signify affection, greeting, reverence, or sexual attraction.

Kissing as a form of greeting or salutation has a long history in Western civilization, with references dating back to the Old Testament, the ancient Greeks and Romans (Roman Catholicism), and the Germanic peoples. Early Christians greeted one another with a kiss, and this “holy kiss” still figures in Roman Catholic rituals; for example, a bishop kisses a newly ordained priest and is himself kissed when he is consecrated. Medieval knights were kissed after being dubbed, and the custom of kissing the bride remains almost universal in Western marriage ceremonies. Kissing in public for purposes of salutation thus has a long history in the West. It was rarely practiced in East Asia, however, where bowing was the all-purpose form of greeting, and kissing was restricted to moments of private intimacy between the sexes. Under Western influence, kissing in public gradually became more common in Japan and China in the late 20th century.

Kissing as a display of affection between the sexes has taken various forms in non-Western cultures. Among the Eskimos (in Canada called Inuit) and traditional Polynesian societies, a kiss involved rubbing noses with each other, while in southeastern India and among the Sami of Europe, the nose is pressed against the other person's cheek while the active partner inhales.

Deep kissing, in which the tongue is used to explore the other person's mouth, usually occurs in an erotic context, either to express affection or as a means of sexual (sexual behaviour, human) arousal. Among primates, kissing as an inducement to sexual readiness is unique to humans and has probably arisen from the latter's upright posture, face-to-face communication, and the availability of the arms for clasping.