The Feast of Pentecost was celebrated 50 days after the Jewish Passover (minus Sabbath days). This was a Jewish festival giving thanks for the first fruits of the corn harvest. Acts 2:1 notes that on the Day of Pentecost, the Holy Spirit descended on Jesus’ disciples. This event was called Pentecost by the early Christian Church. And it is observed today as the birth of the Church.

From “What is Pentecost” The Upper Room