In the Old Testament, Pentecost is known as the Feast of Weeks:
22“And you shall observe the Feast of Weeks, of the first fruits of wheat harvest, and the Feast of Ingathering at the year’s end.” Exodus 34:22.
“When the day of Pentecost has come, they (the Apostles) were all together in one place. And suddenly a sound came from heaven like the rush of a mighty wind, and it filled all the house where they were sitting. And there appeared to them tongues as of fire, distributed and resting on each one of them. And they were all filled with the Holy Spirit and began to speak in other tongues, as the Spirit gave them utterance. Acts 2:1-4”
It is a time of the greater harvest of wheat.
The fulfillment of the Spring Feast of Pentecost took place with the Apostles at that meeting. It is a time that we celebrate the Holy Spirit and its power in our lives.