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A synchronous orbit is an orbit around a body such that the orbiting body's orbital period matches the rotation period of the host body and the orbit's direction is the same as the host body's rotation direction. With deviation from spherical symmetry of the bodies, such an orbit can be resonant and if the bodies should fall into the resonance, they tend to stay in it.
The term geosynchronous orbit refers to such an orbit around Earth, and the term geostationary orbit refers to a particular kind of geosynchronous orbit: circular and aligned with the Earth's equator, in which case it remains over one spot on the Earth's surface. Some satellites are specifically placed in this orbit, for example, to support radio communication links. This requires a specific orbital radius which places it roughly 22,000 miles above the Earth's surface.
Charon orbits Pluto in a synchronous orbit. In such natural cases, tidal locking is a contributing factor, e.g., involving some asymmetry in Pluto's mass. The two are mutually tidally locked, each rotating so as to face the other. Such rotation of a tidally locked body is termed synchronous rotation, i.e., the rotation is synchronized with the orbital period. (Note that when a body orbits another, they are both actually orbiting their center of mass and in some sense, the two bodies are orbiting each other, which is more evident if their masses are similar. In this sense, the Earth is in a synchronous orbit around the Moon.)