Tikkun Leil Shavuot. Tikkun means “correction”, while “Leil Shavuot” means “night of Shavuot.”
Following the Shavuot holiday meal, many people proceed to synagogue for Ma’ariv [the evening service], followed by an all-night (or into-the-night, as many last only until midnight) Torah study session based on the kabbalists‘ [mystics’] practice. This specifically refers to the 16th-century mystics of Safed, Israel, under the leadership of Isaac Luria. Many people recite Ma’ariv before the meal, go home to eat, and return to synagogue for the study session. All in all, Tikkun Leil Shavuot is a relatively recent development.
We remain awake to show that, unlike the situation of our heavy-lidded ancestors at Sinai, there is no need to bring us to our senses; we are ready to receive Torah. The tikkun (which refers both to the study session and to the text used for it) was the only observance developed specifically for Shavuot.