A kiss is the touching of one person's lips to another place, which is used as an expression of affection, respect, greeting, farewell, good luck, romantic affection or sexual desire. The word comes from Old English cyssan "to kiss", in turn from coss "a kiss".
Anthropologists have not reached a consensus as to whether kissing is a learned or an instinctive behavior. Kissing may lead to sexual behaviors. It may be related to grooming behavior also seen between other animals, or arising as a result of mothers premasticating food for their children.