And so they kept the dedication of the altar eight days and offered burnt offerings with gladness...
Hanukkah, also known as the Festival of Lights, is the Hebrew word meaning "dedication" or "celebration."
The miracle of Hanukkah is described in the Talmud, the major text of Jewish teaching. In short, in the year 168 B.C., the Syrian king Antiochus IV seized the holy temple in Jerusalem and dedicated it to the Greek god, Zeus. Judah Maccabee and his soldiers decided to fight back. In the year 165 B.C., after the forces of Antiochus IV had been driven from the Temple, the Maccabees discovered that almost all of the ritual olive oil had been profaned. They found only a single container that was still sealed by the High Priest, with enough oil to keep the menorah in the Temple lit for a single day. They used this, and miraculously, that oil burned for eight days (the time it took to have new oil pressed and made ready).
It's an ancient story of human bravery and God's grace, a holiday worth celebrating each year.