A synchronous orbit is an orbit in which an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body.

A satellite in a synchronous orbit that is both equatorial and circular will appear to be suspended motionless above a point on the orbited planet's equator. However, a synchronous orbit need not be equatorial, nor circular. A body in a nonequatorial synchronous orbit will appear to oscillate north and south above a point on the planet's equator, while a body in an elliptical orbit will appear to oscillate eastward and westward. The combination of these two motions produces a figure-8 pattern as seen from the orbited body.

A synchronous orbit about the Earth that is circular and lies in the equatorial plane is called a geostationary orbit.

Source: From Federal Standard 1037C