Hanukkah means "dedication" in Hebrew and refers to the time in 165 B.C. when a small army of Jews won a battle with a much larger Greek force and liberated the temple in Jerusalem.
It had been occupied by Greek worshipers of Zeus and needed many repairs.
When they attempted to re-light the eternal flame, they had only enough oil for one day.
However, it burned for eight full days, enough time for more oil to be prepared. The temple was re-dedicated to the God of the Jewish people, thus Jews the world over celebrate Hanukkah, or the Festival of Lights.