Was the day of Pentecost a Jewish feast day?

The day of Pentecost was a Jewish feast day, as recorded in Acts chapter 2, where the first example of speaking in tongues occurred. At that time God was still dealing with the nation of Israel, and Pentecost is identified as a Jewish feast day.

Les explains that the day of Pentecost was a Jewish feast day. He points out that Acts chapter 2 records the first example of the gift of speaking in tongues, and that it happened when God was still dealing with the nation of Israel. He notes there are only three times in Scripture when the Holy Spirit delegated this miracle to men. The context also describes the person speaking in an unknown tongue as speaking not to men but to God, in a small spirit, speaking mysteries beyond ordinary human comprehension.

Acts 2:1

And when the day of Pentecost was fully come, they were all with one accord in one place.

What happened right when the day of Pentecost came in Acts 2?

When the day of Pentecost was fully come, the fiftieth day after Passover, the believers were all together with one accord in one place. Suddenly a sound from heaven like a rushing mighty wind came and filled all the house where they were sitting.