It is unlike any kind of asteroid we have ever seen. It is 400 meters (.25 mile) long but narrow. It is only about 40 meters wide and has a reddish tint from the radiation it has been exposed to through its travels. It is thought to have been traveling through interstellar space for hundreds of millions, if not billions of years. Below is a quick video, just over 3 minutes long with more detail if you are interested.
It's going to make its way out of our system almost as fast as it came into it so it's going to be a short lived visit. Unless of course it's an alien... O_O