What was meant by Holy Kiss?

We see Jesus being given a kiss twice in the Gospels: one in Lk 7:38 by the sinful woman on his feet, and the other by Judas Iscariot, most probably on the cheek. Jesus presumably kissed the feet of the Apostles after washing their feet on Last Supper, if the present day re-enactment of the event during the Holy Week reflected the ancient practice. - Both St. Peter and St. Paul exhorted the faithful to greet one another with the 'Holy Kiss' or 'Kiss of Love': as can be seen from Romans 16:16; 1 Corinthians 16:20; 2 Corinthians 13:12; 1 Thessalonians 5:26; and 1 Peter 5:14. - It has been a Catholic tradition for the faithful to kiss the palm of the Bishop on his Pastoral Visit. Similarly, children kiss the palms of the elderly people of the family as a sign of respect. - Given that both St. Peter and St. Paul repeatedly exhorted the faithful to greet one another with the Holy Kiss, it is most likely that the tradition existed among Jesus and the disciples. My question is: **What was meant by Holy Kiss among early Christians and what was its origin?** Are there any ancient extra-biblical writings or modern scholarly material available on the topic?