It is always celebrated on 6 January and commemorates the presentation of the infant Jesus to the Magi, or three wise men. In some countries, it may be known as 'Three Kings Day'.
Interestingly, the bible doesn't mention how many wise men there were - just that three gifts were given and that they came from the east.
The common consensus is that there were between two and twenty wise men. They were likely to have been Zoroastrian Priests. It wasn't until about 500AD that three was accepted to be the standard number of wise men - the reasoning simply due to the number of gifts.
To further complicate matters, the wise men may not even have been men or wise. In 2004, a report by the general synod of the church of England concluded that 'magi' gives no indication as to number, or gender, or even to the level of wisdom.
Epiphany is derived from the Greek word 'epiphaneia' and means manifestation. In religious use, the term means the appearance of an invisible divine being in a visible form.
The celebration of the Epiphany began in the Eastern Church and included a celebration of Christ's birth. However, by the 4th century AD, the various calendar reforms had moved the birth of Christ to 25 December and the church in Rome began celebrating 6 January as Epiphany. Armenian Christians still celebrate the birth of Christ on 6 January.
In Switzerland, Epiphany is a regional holiday in Graubünden, Lucerne, Schwyz, Ticino and Uri.
In Germany, it is a regional holiday in Baden-Württemberg, Bavaria and Saxony-Anhalt.
In Spain and Germany, the holiday is also known as the 'Three Kings' day. For Spanish children, Three Kings day is a bigger event than Christmas, with presents being delivered by the Three Kings on 5 January, giving the children a day to play with their toys and presents, before school starts again on 7 January.
In Colombia, Epiphany will be celebrated on the Monday after 6 January, if 6 January does not fall on a Monday.
In Denmark, Epiphany was abolished as an official church festival in 1770. However, the previous evening, Twelfth Night, is celebrated in some homes by burning a special Twelfth Night candle with three wicks. When the candles thus go out, it symbolises the end of Christmas. A very few locations in Denmark still celebrate the evening with a procession where people in fancy dress and go from house to house.
In Greece, celebrations include the traditional blessing of the waters. This is particularly striking in Piraeus, where the diver who retrieves a cross-thrown into the water by the local priest is blessed with good luck throughout the year.
The period between Christmas Day and Epiphany is known as the Twelve Days of Christmas as celebrated in the popular Christmas carol of the same name.