Kissing is the action of pressing one's lips against something or someone as a sign of affection.
The meaning of a kiss can vary considerably. In many cultures kissing on the mouth is a private and intimate expression of love and desire by courting or married couples. Kissing somebody on the cheek or forehead is a sign of affection, for example between family members. In some formal settings, gentlemen are expected to kiss the hand of a lady when introduced. Kissing a ring on the hand of a bishop or royal is a sign of respect or devotion. There is a longstanding Roman Catholic tradition of kissing the Pope's ring in this way.
People sometimes kiss inanimate objects such as their own possessions as an eccentric display of affection or gratitude to them. Prostrating oneself and kissing the ground can be an expression of relief shown by those returning to their homeland after a long absence. Pope John Paul II was noted for kissing the ground on arrival at various airports on his Papal visits.
Kissing has been practiced throughout human history, in virtually all cultures of the world. Humans are believed to be the only creatures that kiss, although mouth contact is observed among the courtship rituals of some mammals and birds, including pigeons.
Kissing people of the same sex is often considered socially inappropriate, and sometimes even considered taboo because of its association with homosexuality. However, in many cultures, including France, Italy, Russia, Egypt and some other countries, it is common to greet friends of either sex with a kiss - usually on the cheek - as a sign of platonic friendship. This was also customary in Biblical times, when Judas Iscariot used a kiss as the signal to have Jesus arrested.