Shavuot was originally an ancient harvest festival celebrating the grain crop. In Hebrew, Shavuot means "weeks" and the holiday is celebrated seven weeks after Passover begins. But Shavuot is also recognized as the anniversary of the giving of the Torah on Mt. Sinai and most Shavuot celebrations are centered on Torah study and other Jewish learning. On the first night of the holiday many people stay up all night studying Jewish texts.
There is a custom of eating dairy foods--especially cheesecakes and blintzes--on Shavuot. The reason for this tradition is not entirely clear, but one popular explanation is that immediately after the Israelites received the Torah and learned about the laws of keeping kosher, it was too complicated for them to begin butchering and preparing fresh kosher meat. So they stuck with eating dairy--and now we do the same on Shavuot to commemorate this.
In synagogue on Shavuot the Book of Ruth is read. Ruth is a non-Israelite who embraces Judaism, and her personal acceptance of the Jewish faith is considered analogous to the Israelites’ communal acceptance of the Torah at Sinai. In keeping with the conversion theme, many congregations hold programs on Shavuot that welcome new converts, or discuss the laws of conversion.