Therefore it always occurs on a Sunday. It is also the tenth day after Ascension Thursday, which itself is 40 days from Easter, counting inclusive of Easter Sunday itself.
The Christian Pentecost is based on the New Testament, where it refers to the descent of the Holy Spirit upon the Apostles and other followers of Jesus Christ, as described in the Acts of the Apostles 2:1–31. According to Luke 22:12–13, the descent of the Holy Spirit occurred while the Apostles were celebrating the Jewish day of Shavuot, the Feast of Weeks, a prominent feast in the calendar of ancient Israel celebrating the giving of the Law to Moses at Sinai. Subsequently, Pentecost may refer to the Pentecost of the New Testament and Shavuot of the Old Testament. Shavuot is a significant event shared by Jews and Christians but Christians do not commonly celebrate it as a separate holiday.
In the Christian liturgical year it became a feast commemorating what is described by some Christians as the Birthday of the Church.
The holy day is also called White Sunday or Whitsunday, especially in the United Kingdom, where traditionally the next day, Whit Monday, was also a public holiday. In Eastern Christianity, Pentecost can also refer to the entire fifty days of Easter through Pentecost inclusive; hence the book containing the liturgical texts for Paschaltide is called the Pentecostarion.
In Germany Pentecost is denominated Pfingsten and often coincides with scholastic holidays and the beginning of many outdoor and Spring activities, such as festivals and organized outdoor activities by youth organizations. The Monday after Pentecost is a legal holiday in many European nations.