For those of you who may not be as familiar with Chanukah, chabad.org provides a nice little summary of what Chanukah commemorates. They write:
More than twenty-one centuries ago, the Holy Land was ruled by the Seleucids (Syrian-Greeks), who sought to forcefully Hellenize the people of Israel. Against all odds, a small band of faithful Jews defeated one of the mightiest armies on earth, drove the Greeks from the land, reclaimed the Holy Temple in Jerusalem and rededicated it to the service of G-d.So basically it boils down to the same thing a lot of Jewish holidays celebrate - They tried to kill us. We survived. Let's eat!
When they sought to light the Temple's menorah (the seven branched candelabrum), they found only a single cruse of olive oil that had escaped contamination by the Greeks; miraculously, the one-day supply burned for eight days, until new oil could be prepared under conditions of ritual purity. To commemorate and publicize these miracles, the sages instituted the festival of Chanukah. At the heart of the festival is the nightly menorah (candelabrum) lighting: a single flame on the first night, two on the second evening, and so on till the eighth night of Chanukah, when all eight lights are kindled.