Pentecost (“the fiftieth day”) is a Christian holiday commemorating the descent of the Holy Spirit upon the Apostles on the fiftieth day after the resurrection of Jesus Christ, and the end of the season of Easter. The Apostles began to speak in many languages and have received other spiritual gifts. The event was foretold by Jesus before his Ascension.
In Christian tradition Pentecost is a moveable feast observed exactly seven weeks after Easter Day, i.e. 50 days after Easter (inclusive, 49 + Easter). It always falls on the seventh Sunday after Easter Day. In Eastern churches the date of Pentecost is calculated in the same manner but it usually differs due to the use of the Julian calendar instead of the Gregorian. Pentecost is a holy day of obligation in the Catholic Church.