Hanukkah is a Jewish celebration observed by lighting candles, reciting blessings, singing songs and family gatherings. Also known as the Festival of Lights or Feast of Dedication , is an eight-day Jewish holiday beginning on the 25th day of Kislev according to the Hebrew calendar, which may fall anytime from late November to late December. It celebrates the rededication of the Second Temple at the time of the Maccabee rebellion.

Each evening at sundown, the Hanukkah menorah is lit. The menorah has 9 candles. The one in the middle (called the Shamash – or Servant Candle) is used to light all the others. The other eight (4 on each side, and a little lower than the Shamash) are for each of the eight days that the Temple flame miraculously burned. On the first night, only the far right candle is lit. The second night, two candles are lit starting at the far right. The third night, three candles, and so it goes until the eighth and final night when all eight candles are lit. They are lit for a half hour, during which we do no work, but instead we remember the work of God (His miracles and providence) and praise Him.
(wikipedia.org, centralpc.org, musiced.about.com)