Pentecost originated as a Jewish holiday that fell 50 days after Passover. Its purpose was to thank God for the harvest. Members of the Christian religion mark Pentecost as the day when the Holy Spirit came to Earth, 40 days after Easter Sunday.
Acts 2 details the story of the arrival of the Holy Spirit, Peter and some other members of the early Church were in Jerusalem to celebrate the Jewish holiday of Pentecost. When they gathered together on that day, the house in which they had gathered was filled with the sound of a tumultuous wind which seemed to take over the whole building. They also thought they saw fiery tongues that split up and landed on the heads of all in the room before they all started talking in different languages through the power of the Holy Spirit.
Pentecost is not as prominent on North American church calendars as it is in Europe, where it is treated as a major feasting day. Also known as Whitsuntide in some parts of Europe, it ranks only behind Easter in total significance. It is treated as a two-day religious holiday in several parts of Europe, as are both Easter and Christmas.