Feast of Pentecost
The feast of Pentecost was in NT times the name for the celebration of the Feast of Weeks because it occurred on the fiftieth day after Passover. It was a one-day festival in which special sacrifices were offered, and originally it was a harvest (firstfruits) festival (Exod. 23:16;34:22; Lev. 23:15–21; Num. 28:26; Deut. 16:9–12). It is possible, but not certain, that as early as this time this festival was associated with the giving of the Law on Sinai.
Witherington, Ben, III. The Acts of the Apostles: A Socio-Rhetorical Commentary. Grand Rapids, MI: Wm. B. Eerdmans Publishing Co., 1998. Print.