What on Earth is space junk?

Space junk is basically anything up there that's not working and functional. Things orbit the Earth at several miles a second. So, even something quite small, like a--a fleck of paint or a--you know, a screw, when it hits at several miles a second, it hits with a lot of energy. And satellites have been destroyed. As far as actually going up there and cleaning it up, that's going to be a very expensive thing. And it's not really clear yet as to what, as to how that would actually be done. But, at some point, it probably would have to be done, because the problem is going to--of space junk--is going to get worse and worse because the junk collides with each other and 2 pieces collide with each other and 10 pieces come out.