On the 25th of Kislev in the year 3622 from creation, the Maccabees liberated the Holy Temple in Jerusalem, after defeating the vastly more numerous and powerful armies of the Syrian-Greek king Antiochus IV, who had tried to forcefully uproot the beliefs and practices of Judaism from the people of Israel. The victorious Jews repaired, cleansed and rededicated the Temple to the service of G-d. But all the Temple's oil had been defiled by the pagan invaders; when the Jews sought to light the Temple's menorah (candelabra), they found only one small cruse of ritually pure olive oil. Miraculously, the one-day supply burned for eight days, until new, pure oil could be obtained. In commemoration, the Sages instituted the 8-day festival of Chanukah, on which lights are kindled nightly to recall and publicize the miracle.

Link: The Story of Chanukah

The eighth day of Chanukah is also known as Zot Chanukah (lit., "this is Chanukah"), after a key phrase in the special Chanukah Torah reading for this day (Numbers 7:54-8:4). For the deeper significance of this name, see link to "Accumulating Lights" below.

In the Jewish calendar, the day begins at nightfall; thus, the last kindling of the Chanukah lights is held on the evening preceding the 8th day of Chanukah, when eight lights are lit (see "Laws & Customs" for yesterday's date). The festival of Chanukah concludes at nightfall this evening.

It is customary, however, to light candles during the daytime as well, in synagogues, in public spaces, and at gatherings held in honor of the festival. These lightings are done without recitation of the blessings as they do not constitute an observance of the mitzvah of kindling the Chanukah lights.

Other Chanukah observances include the inclusion of Hallel and Al Hanissim in the daily prayers, eating food fried in oil and dairy foods, playing with the "dreidel" and giving gifts of money ("Chanukah gelt") to children.

Links: Accumulating Lights