Definitions for "Synchronous orbit"
A satellite is in synchronous orbit (also called synchronous rotation) when its orbital period is the same as its period of rotation about its axis. The Moon is in a synchronous orbit, so the same side of the moon always faces Earth.
a circular orbit around the Earth's equator, at a distance of 6.6 Earth radii. At this distance the orbital period is 24 hours, keeping the satellite "anchored" above the same spot on Earth. This feature makes the synchronous orbit useful for communication satellites: a satellite transmitting TV programs to the US, for instance, will always be in touch with the US if "anchored" above it, and receiving antennas on the ground only need to point to one fixed spot in the sky.
The orbit over the earth's equator at an altitude of 36,000 km, in which the rate of revolution of the satellite around the earth equals the rate of rotation of the earth, so that the satellite always stays over the same spot on the ground.