Since the Rabbinic period, Shavuot has been tied to the story of the Israelites receiving the Torah at Sinai. Because of this, Shavuot has come to be dedicated to the idea of Torah study and Jewish education. One custom is an all-night (or late night) study session held on the first evening of the festival, called Tikkun Leil Shavuot. This custom had its beginning in the Safed kabbalist community around the 16th century and is designed to prepare Jews for “receiving” the Torah again on Shavuot.
See also:
What is a Confirmation?
Tikkun Leil Shavuot Videos and Study Guides