A medium Earth orbit (MEO) is an Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between 2,000 and 35,786 km above sea level.
To-scale diagram of low, medium, and high Earth orbits
A geosynchronous orbit is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds. The synchronization of rotation and orbital period means that, for an observer on Earth's surface, 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 may remain still or trace out a path, typically in a figure-8 form, whose precise characteristics depend on the orbit's inclination and eccentricity. A circular geosynchronous orbit has a constant altitude of 35,786 km (22,236 mi).
The geosynchronous orbit was popularised by the science fiction author Arthur C. Clarke, and is thus sometimes called the Clarke Orbit.
Syncom 2: The first functional geosynchronous satellite
A quasi-zenith satellite orbit
A computer-generated image of space debris. Two debris fields are shown: around geosynchronous space and low Earth orbit.