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Epiphany (Koine Greek: Ἐπιφάνεια, Epiphaneia, "Manifestation", "striking appearance")[1] or Theophany[2] (Ancient Greek: (ἡ) Θεοφάνεια, Τheophaneia meaning "Vision of God"),[3] also known as Three Kings' Day,[4] is a Christian feast day that celebrates the revelation of God in his Son as human in Jesus Christ. In Western Christianity, the feast commemorates principally (but not solely) the visit of the Magi to the Christ child, and thus Jesus' physical manifestation to the Gentiles.[5][6] Moreover, the feast of the Epiphany, in some Western Christian denominations, also initiates the liturgical season of Epiphanytide.[7][8] Eastern Christians, on the other hand, commemorate the baptism of Jesus in the Jordan River, seen as his manifestation to the world as the Son of God.[9]

The traditional date for the feast is January 6.

In many Western Christian Churches, the eve of the feast is celebrated as Twelfth Night.[12][13] The Monday after Epiphany is known as Plough Monday.[14]

Catholic encyclopedia on the topic: https://www.newadvent.org/cathen/05504c.htm

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On the Feast of the Epiphany in some parts of central Europe the priest, wearing white vestments, blesses Epiphany water, frankincense, gold, and chalk. The chalk is used to write the initials of the three magi over the doors of churches and homes. The letters stand for the initials of the Magi (traditionally named Caspar, Melchior, and Balthasar), and also the phrase Christus mansionem benedicat, which translates as "may Christ bless the house".