Shavuot is a Jewish religious holiday.
The Shavuot celebration originated in Israel and they celebrate a feast.
No. Tefillin are not worn on holidays, including Shavuot, or on the Sabbath.
Shavuot (mistranslated as Pentecost) was fifty days after the Passover. Still is.
No. Anything dairy is traditional on Shavuot, especially blintzes.
Shavuot is recognized as a festival by all branches of Judaism, Orthodox, Reform, Conserviative. However, of the three pilgrimage festivals, it is the most frequently ignored. (Despite the good food, since cheesecake is a traditioinal food for Shavuot.) I have been to Orthodox synagogues where hardly anyone showed up for Shavuot, and I have been to Reform synagogues that were crowded on Shavuot. Even so it is probable that more Orthodox Jews take Shavuot seriously.
Yes, Shavuot is a Jewish holy day/festival (Leviticus ch.23).
The custom is not to pray all night, but to study all night. Shavuot is considered to be the anniversary of the Giving of the Torah at Mount Sinai. Tikkun Leil Shavuot is the custom of staying up the entire night (leil) of Shavuot studying with the community in order to reexperience standing at Sinai.
Judaism
On Shavuot
Jewish culture
It originated in the Jewish religion.