Pentecost
Pentecost (Ancient Greek: Πεντηκοστή [ἡμέρα], Pentēkostē [hēmera], "the fiftieth [day]") is the Greek name for Shavuot (Hebrew: שבועות, lit. "Weeks"), the Feast of Weeks, a prominent feast in the calendar of ancient Israel celebrating the giving of the Law to Moses at Sinai. In Christianity, Pentecost is celebrated fifty days after Easter Sunday, inclusively (i.e., 49 days with the first day counted, seven weeks), hence its name. In Judaism, Shavuot is on the sixth day of the Hebrew month of Sivan (late May or early June). Pentecost falls on the tenth day after Ascension Thursday (which itself is 40 days after Easter).
The feast 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 between Easter and Pentecost, hence the book containing the liturgical texts for Paschaltide is called the Pentecostarion.
In the New Testament, Pentecost was the occasion of 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. and therefore in the Christian liturgical year, it became a feast commemorating this occasion. For this reason, Pentecost is described by some Christians as the "Birthday of the Church". The Pentecostal movement of Christianity derives its name from this New Testament event, as the movement emphasizes direct personal experience with God, akin to the Descent of the Holy Spirit upon the Apostles.