Plain English Meaning
An orbit where a satellite circles the Earth at the same speed the Earth turns, so it stays above roughly the same spot on the ground all the time.
Full Definition
An orbit around Earth in which a satellite completes one revolution in the same time it takes Earth to rotate once on its axis — approximately 24 hours — at an altitude of about 22,236 miles above the equator. A satellite in this orbit appears to stay over the same general region of Earth, allowing continuous communication and data coverage of that area.
Context Anchor
Pilots may encounter this term in discussions of weather satellites, satellite communication, and services that depend on satellites staying in view of a large region.
Derivation
From Greek 'geo' meaning Earth, and 'synchronous' meaning happening at the same time. The satellite's orbit is synchronised with Earth's — they move together.