What is Hanukkah?
Hanukkah is a Jewish holiday celebrated for eight days and nights. It starts on the 25th of the Jewish month of Kislev, which coincides with late November-late December on the secular calendar. In Hebrew, the word “hanukkah” means “dedication.” The name reminds us that this holiday commemorates the re-dedication of the holy Temple in Jerusalem following the Jewish victory over the Syrian-Greeks in 165 B.C.E.
Once the Maccabees had regained control they returned to the Temple in Jerusalem. By this time it had been spiritually defiled by being used for the worship of foreign gods and also by practices such as sacrificing swine. Jewish troops were determined to purify the Temple by burning ritual oil in the Temple’s menorah for eight days. But to their dismay, they discovered that there was only one day's worth of oil left in the Temple. They lit the menorah anyway and to their surprise the small amount of oil lasted the full eight days.
This is the miracle of the Hanukkah oil that is celebrated every year when Jews light a special menorah known as a hanukkiyah for eight days. One candle is lit on the first night of Hanukkah, two on the second, and so on, until eight candles are lit. You can learn more about the hanukkiyah in the article: What Is a Hanukkiyah?