The Pentecost feast is also called Whit Sunday, especially in England, where the following Monday was traditionally a holiday. Pentecost is celebrated seven weeks (50 days) after Easter Sunday, hence its name. Pentecost is also the old Greek and Latin name for the Jewish harvest festival, or Festival of Weeks.
According to Jewish tradition, Pentecost commemorates God giving the Ten Commandments at Mount Sinai fifty days after the Exodus. It is also said that a building on Mount Zion is traditionally revered by Jews and by Christians as David’s Tomb (or the Cenacle meaning the upper room) and that there is a Jewish tradition that David was born and died on Pentecost.
It is in this upper room where the 12 Disciples of Christ along with about 108 other individuals, including many women, among whom was Mary the mother of Jesus received the Baptism of the Holy Spirit on Pentecost.
Traditional interpretation holds that the Descent of the Holy Spirit took place in the Upper Room, or Cenacle while celebrating the day of Pentecost. The Upper Room was first mentioned in Luke 22:12-13 and is where they prepared for the first feast of Passover. This Upper Room was also to be the location of the Last Supper and the giving of Holy Communion.
Since Pentecost itself is on a Sunday, it is automatically a public holiday almost everywhere. Additional restrictions to Sunday opening hours may apply.
Pentecost Monday is a public holiday in many European countries including Austria, Belgium, Cyprus, Denmark, Estonia, France, Germany, Greece, Hungary, Iceland, Luxembourg, the Netherlands, Norway, Romania. In the United Kingdom the day is known as Whit Monday, and was a bank holiday until 1967 when it was replaced by the Spring Bank Holiday.
To finish according to legend, King Arthur always gathered all his knights at the round table for a feast and a quest on Pentecost:
My thanks to Wikipedia for help with dates.