synchronous orbits have been seperated from the other types of orbit in the LEO class of orbit because of their uniqueness and prevalence; These orbits slice vertically down the Earth from north to south all within 4 degrees of inclination.
Rather than having a consistent longitude as seen from Earth, like Geo-synchronous orbits, the consistency is in their position relative to the Sun; Meaning if you were standing on the Sun the satellite would follow the exact same path around the Earth regardless of the Earth's rotating or revolving beneath.