Hanukkah is a Jewish holiday commemorating the rededication of the Holy Temple (the Second Temple) in Jerusalem at the time of the Maccabean Revolt against the Seleucid Empire. Hanukkah is observed for eight nights and days. It is also known as the Festival of Lights and the Feast of Dedication.
The dates of Hanukkah are determined by the Hebrew calendar. Hanukkah begins at the 25th day of Kislev, and concludes on the 2nd or 3rd day of Tevet (Kislev can have 29 or 30 days). The Jewish day begins at sunset, whereas the Gregorian calendar begins the day at midnight. Hanukkah begins at sunset of the date listed.
The festival is observed by the kindling of the lights of a unique candelabrum, the nine-branched menorah, one additional light on each night of the holiday, progressing to eight on the final night. The typical menorah consists of eight branches with an additional visually distinct branch.
Other Hanukkah festivities include playing dreidel and eating oil-based foods such as doughnuts and latkes.
Source: wikipedia.org
In 2017 Hanukkah in USA falls on December 13.