Space debris is the collection of defunct man-made objects in space--old satellites, spent rocket stages, and fragments from disintegration, erosion, and collisions--including those caused b debris itself.
As of July 2013, there are over 170 million debris smaller than half an inch. About 19 thousand have been tracked. Space debris are denser than meteoroids; mostly dust from solid rocket motors, surface erosion debris like paint flakes, and frozen coolant from RORSAT nuclear-powered satellites. They cause damage akin to sandblasting, especially to solar panels and optics like telescopes or star trackers that cannot be covered with a ballistic Whipple shield (unless it is transparent).
For comparison, the international space station orbits in the 300 to 400 kilometers range and the 2009 satellite collision and 2007 antisat test occurred at 800 to 900 kilometers. The ISS has Whipple Shielding, however known debris with a collision chance over 1 in 10,000 are avoided by maneuvering the spacecraft.
Beyond a critical density, Kessler Syndrome ensues--a runaway chain reaction of collisions exponentially increasing the amount of debris. This affects useful polar-orbiting bands, increases the cost of protection for missions and destroys live satellites. Whether it is underway is debated. The measurement, mitigation and potential removal of debris are conducted by some participants in the space industry.
A geosynchronous orbit is an orbit around the Earth with an orbital period of one sidereal day, intentionally matching the Earth's sidereal rotation period. The synchronization of rotation and orbital period means that, for an observer on the surface of the Earth, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day. Over the course of a day, the object's position in the sky traces out a path, typically in a figure eight form, whose precise characteristics depend on the orbit's inclination and eccentricity.