What is the Christian Greeting ?

It was the widespread custom in the ancient western Mediterranean for men to greet each other with a
kiss. That was also the custom in ancient Judea and practiced also by Christians.

However, the New Testament's references to a holy kiss (Greek: εν αγιω φιληματι, en philemati hagio) and
kiss of love (en philemati agapēs) transformed the character of the act beyond a greeting. Such a kiss is
mentioned five times in the concluding section of letters in the New Testament:

Romans 16:16 — "Greet one another with a holy kiss"
1 Corinthians 16:20 — "Greet one another with a holy kiss"
2 Corinthians 13:12 — "Greet one another with a holy kiss"
I Thessalonians 5:26 — "Greet all the brothers with a holy kiss"
1 Peter 5:14 — "Greet one another with a kiss of love"

It has been noted that these mentions of the holy kiss come at the end of these epistles. Since these
epistles were addressed to Christian communities they would most probably have been read in the context
of their communal worship. If the assemblies for worship already concluded in a celebration of the
Eucharist the holy kiss would already have occurred in the position it would later occupy in most ancient
Christian liturgical tradition (with the exception of the Roman Rite), namely after the proclamation of the
Word and at the beginning of the celebration of the Eucharist.[citation needed]

The writings of the early church fathers speak of the holy kiss, which they call "a sign of peace", which was
already part of the Eucharistic liturgy, occurring after the Lord's Prayer in the Roman Rite and the rites
directly derived from it. St. Augustine, for example, speaks of it in one of his Easter Sermons:
Then, after the consecration of the Holy Sacrifice of God, because He wished us also to be His sacrifice, a fact
which was made clear when the Holy Sacrifice was first instituted, and because that Sacrifice is a sign of
what we are, behold, when the Sacrifice is finished, we say the Lord's Prayer which you have received and
recited. After this, the 'Peace be with you’ is said, and the Christians embrace one another with the holy kiss.
This is a sign of peace; as the lips indicate, let peace be made in your conscience, that is, when your lips
draw near to those of your brother, do not let your heart withdraw from his. Hence, these are great and
powerful sacraments.

From an early date, to guard against any abuse of this form of salutation, women and men were required to
sit separately, and the kiss of peace was given only by women to women and by men to men.

The practice remains a part of the worship in traditional churches, including the Episcopal Church, Roman
Catholic Church, Eastern Catholic Churches, Eastern Orthodox churches, Oriental Orthodox churches;
some liturgical mainline Protestant denominations; and Spiritual Christian, where it is often called the kiss
of peace, sign of peace, Holy kiss or simply peace or pax; It is practiced as a part of worship in many
Anabaptist heritage groups including Old German Baptist Brethren, and Apostolic Christian.

Article taken from wikipedia.org