Space debris

I was doing some research this afternoon on the company that I'm interviewing with on Tuesday, and they have a short animation on their website that shows all the tracked objects that are in orbit around the Earth. It's really crowded out there! Okay, yes, I understand that it looks more crowded because it's a 3D projection onto a flat screen, but still! It would be interesting to know which ones are actually in use and which ones are just space junk.