Feast Of Weeks or Pentecost
This occurred in late spring seven weeks after Passover and the ingathering of the first harvest eg Wheat.
According to oral tradition, the Feast of Weeks was the time of giving The Torah or The Law of Moses at Mount Sinai.
In the New Testament this was the time when the Holy Spirit came upon the disciples, as promised by Jesus, and there was a harvest of new believers.
Feast Of Weeks or Pentecost along with Passover and Feast of Trumpets make up the three sets of feast God gave Israel to keep.
Feast of Weeks
God said to Moses 26 "On the day of firstfruits, when you present to the LORD an offering of new grain during the Feast of Weeks, hold a sacred assembly and do no regular work. 27 Present a burnt offering of two young bulls, one ram and seven male lambs a year old as an aroma pleasing to the LORD. 28 With each bull there is to be a grain offering of three-tenths of an ephah of fine flour mixed with oil; with the ram, two-tenths;29 and with each of the seven lambs, one-tenth. 30 Include one male goat to make atonement for you. 31 Prepare these together with their drink offerings, in addition to the regular burnt offering and its grain offering. Be sure the animals are without defect.
Feast of Weeks or Shavuot in New Testament is called Pentecost coming 50 days after Passover or Unleaven Bread."