The word Chanuka means 'dedication' and it is widely used in this sense in phrases like 'Chanukat haBayit', dedication of one's home.
So, what 'dedication' are we referring to in the Festival of Chanuka?
During the Second century BCE the Jews were subjugated by the Syrian-Greek army of Antiochus Epiphanies. They were not permitted to practice their religion . The Holy Temple of Jerusalem (Bet haMikdash), was captured and defiled by the Greeks.
They introduced an image of Zeus Olympus, and dedicated our Holy Temple to him, offering sacrifices of impure animals like pigs. In the years 165 BCE the Jews lead by Yehuda Maccabi rebelled against the powerful armies of Antiochus and miraculously defeated them. Their first mission was to recover the Bet haMikdash. They purified the Holy Temple and in order to dedicate it to God Almighty they needed to light the Menorah, to indicate that the Bet haMikdash was operating to God's service. They found one small jar, with an amount of oil which normally would last only for one night.
They lit the Menorah and joyfully rededicated the Bet haMikdash back to God. Miraculously, the oil lasted for eight days, the exact time needed to produce new pure olive oil.
Chanuka means the 'dedication of the Bet haMikdash' to God Almighty, after years of being defiled.
Chanuka is observed by the kindling of candles during the nights of the holiday, in remembrance of the miracle of the oil.
Chanuka is celebrated on the 25th of the month of Kislev. This year, 2010, Chanuka starts Wednesday Dec 1st at night.
The story of Chanuka, from The History Channel: http://www.history.com/videos/history-of-hanukkah#history-of-hanukkah
Rabbi Yosef Bitton. YMJC 130 Steamboat Rd. Great Neck NY 11024