Easter Sunday, 10 days after Ascension Day. It was the Greek name for the Jewish festival of Shavuot, although the dates for the two celebrations rarely correspond.
In the Orthodox church, Pentecost falls on the same day as Trinity Sunday.
Pentecost is also known as Whitsunday (the old-English for White Sunday) in the UK and other English speaking areas.
The day after Pentecost is sometimes called Whit Monday and is a holiday in many countries.
Pentecost celebrates the coming of the Holy Spirit as described in Acts, Chapter 2, when tongues of fire are said to have descended from heaven causing the disciples to start speaking in many different languages and leading to the conversion of some 3,000 witnesses.
Pentecost is observed in churches across the world, but customs differ from country to country. Italian celebrations feature rose petals; the French blow trumpets to simulate a mighty wind; horse-racing and Whitsun ales used to be a major element in England, suppressed by the Puritans; In Poland people decorate their houses with green branches. In the Eastern Orthodox Church the whole week is regarded as an ecclesiastical feast and celebration.