Nuts. It's been rainy and cold here in NorCal, and so I almost totally forgot about the Geminids! No, they're not Cylons from Gemenon. They're meteors from Phaethon!
Seriously, this is the only known meteor shower linked with an asteroid as opposed to a comet. As I wrote recently, meteor showers come from comets. As the comet is warmed by the Sun, it slowly breaks up and leaves, well, crap in its wake: gravel, dust, chunks of ice. These orbit the Sun, and sometimes the Earth plows through them. We get lots of meteors, and it's called a shower.
But in the case of the Geminids, the orbits match that of an actual asteroid named Phaethon, a big ol' chunk of rock that happens to orbit the Sun on a path that takes it pretty close to ours. This is odd, to say the least, but one possible explanation is that Phaethon used to be a comet, but lost all its ice. Now all that's left is a rock, which looks asteroidish. Many other objects have characteristics that blur the line between asteroids and comets, like Chiron. Maybe Phaethon is just a little bit more advanced.