The Feast of Weeks comes 50 days, or seven weeks and a day, after the Sunday within the Week of Unleavened Bread. Our ancestors would make offerings of crops to the Most High and also other offerings. This celebration is also called, Feast of Harvest (Exodus 23:16), Day of First Fruit (Numbers 28:26) and Pentecost (Acts 2:1).
Always remember, the appointed times that Yah gave our ancestors are ALL a shadow of Yahushua (Jesus) [Colossians 2:17]. This is why the Messiah died on Passover, was in the grave during the week of Unleavened Bread and three days after His death He rose according to the First Fruit Sheaf Waving. Then seven weeks later He gave the promise of the Spirit to the apostles on Pentecost. This is why the apostle James refers to himself and the other apostles as a kind of first fruits (James 1:18) fulfilling the Day of First Fruit in the Messiah.