Tu BiShvat (ט״ו בִּשְׁבָט) is a Jewish holiday celebrated on the 15th day of the Hebrew month of Shevat. They are also known as Rosh HaShanah La'Ilanot (ראש השנה לאילנות), meaning "New Year of the Trees". The term "Tu BiShvat" is derived from its Hebrew date, the fifteenth day of Shevat, represented by the Hebrew letters Tet and Vav, equating to 15 numerically. It is also referred to as "Chamisha Asar BiShvat" (חמשה-עשר בשבט, 'Fifteenth of Shevat'). Tu BiShvat appears in the Mishnah in Tractate Rosh Hashanah as one of the four new years in the Jewish calendar. The first of Shevat is the "new year for trees," according to the school of Shammai; the school of Hillel, however, places this on the fifteenth of Shevat. The rabbis ruled in favor of Hillel on this issue, and the 15th of Shevat became the date for calculating the beginning of the agricultural cycle for biblical tithes. In the Middle Ages, Tu BiShvat was celebrated with a feast of fruits in keeping with the Mishnaic description of the holiday as a "New Year." In the 16th century, the kabbalist Rabbi Rav Yitzchak Luria of Safed (Arizal) and his disciples instituted a Tu BiShvat seder in which the fruits and trees of the Land of Israel were given symbolic meaning. The main idea was that eating ten specific fruits and drinking four cups of wine in a particular order while reciting the appropriate blessings would bring human beings and the world closer to spiritual perfection. In many communities, the kabbalistic Tu BiShvat seder has been revived and is now celebrated by many Jews, religious and secular. Special haggadot have been written for this purpose.[citation needed] In the Hasidic community, some Jews pickle or candy the etrog (citron) from Sukkot and eat it on Tu BiShvat. Some pray they will be worthy of a beautiful etrog on the following Sukkot. Some Jews prepare a dessert of grains, dried fruits, and nuts to celebrate the holiday.