What is space debris and why is it an issue?
Any human-made object in orbit about the Earth that no longer serves a useful function.
NASA - Space Debris
Low earth orbit (LEO) is an orbital space junk yard. There are millions of pieces of space junk flying in LEO. Most orbital debris comprises human-generated objects, such as pieces of space craft, tiny flecks of paint from a spacecraft, parts of rockets, satellites that are no longer working, or explosions of objects in orbit flying around in space at high speeds.