Shavuot is the holiday which commemorates God’s giving us the Torah at Mt. Sinai.
Shavuot is a Yom Tov, meaning that its observance is identical to Shabbat, except that cooking and public carrying are permitted. Shavuot literally means “weeks” and it is so named because its date is determined by counting exactly seven weeks from the second day of Pesach. During these seven weeks we count the Omer, which is a measure of barley brought as an offering during the time of the Temple in Jerusalem. Shavuot, in addition to being the day on which the Torah is given, is also the date marking the conclusion of the annual barley harvest.
One Shavuot custom is to stay up late on the first night of the holiday to study the Torah and other biblical and rabbinic texts. This custom is known as Tikkun Leil Shavuot.
Another custom is the reading of the biblical Book of Ruth. Ruth connects to Shavuot in a number of ways. The story takes place during the time of the barley harvest. Ruth is known as one who accepted the Torah upon herself, similar to what all of Israel did at Sinai. Finally, Ruth’s story concludes with a reference to her great grandson, King David. David, according to Jewish tradition, was born and died on Shavuot.