Any orbit taking one sidereal day is geosynchronous; geostationary is the special geosynchronous orbit that is circular and over the equator, so it stays still overhead.
Both words describe orbits that take one sidereal day — 23 hours 56 minutes 4 seconds — to go round Earth. A satellite in any such orbit comes back to the same point in the sky at the same time every day. That makes it geosynchronous.
If the orbit is also circular and lies over the equator, the satellite does not just return each day. It never moves at all, as seen from the ground. That special case is geostationary. Every geostationary orbit is geosynchronous, but not every geosynchronous orbit is geostationary.
India's NavIC constellation has seven satellites. Three are geostationary, at 32.5°E, 83°E and 129.5°E. The other four are geosynchronous but tilted 29° to the equator, two in each of two orbit planes. One plane crosses the equator at 55°E and the other at 111.75°E.
The catalogue shows the difference clearly. IRNSS-1I, one of the tilted ones, has an inclination of 29.07° and a period of 1,436.15 minutes. NVS-01 has the same kind of period, 1,436.02 minutes, but an inclination of only 1.84°.
A satellite in a tilted geosynchronous orbit appears to trace a figure of eight once every orbit. It swings as far north and south as its inclination — up to 29° for NavIC's tilted satellites — and drifts a little east and west of its crossing longitude along the way.
The east–west wobble happens because the satellite's motion is partly north–south. Near the equator it moves eastward a little slower than the ground below; near the top and bottom of its swing it moves eastward faster than the ground there. So it runs behind, then ahead, twice in each day.
Both kinds share the same period, about 1,436 minutes, and nearly the same height. The difference shows up in the inclination column: near 0° for geostationary satellites such as INSAT-3DS (0.10°), and well above it for tilted ones such as IRNSS-1I (29.07°).
A dish aimed at a tilted geosynchronous satellite would have to follow it around the sky. That is why fixed TV dishes are pointed only at geostationary satellites.
NVS-03 is bound for a tilted geosynchronous orbit: over a day its estimated position swings north and south of the equator instead of staying put. Follow NVS-03
Take a circular geosynchronous orbit of inclination i. Measure the satellite's position by u, the angle travelled since it crossed the equator going north. Because the period equals Earth's rotation period, u also equals the angle Earth has turned.
Spherical trigonometry gives the satellite's latitude φ and its longitude λ east of the crossing point:
sin φ = sin i · sin u λ = atan2(cos i · sin u, cos u) − u
The first line says the latitude swings between +i and −i. The second line is zero at u = 0°, 90°, 180° and 270°, and in between it is a small east–west offset. Two north–south swings plus two east–west wobbles per day draw the figure of eight.
Worked numbers for NavIC's i = 29°: the latitude reaches ±29°. Evaluating λ numerically over a full orbit gives a largest offset of about 3.8° of longitude. So the eight is tall and narrow: about 58° of latitude from end to end but only about 7.7° wide.
Eccentricity adds a second effect. IRNSS-1I's catalogue orbit is 35,699 × 35,876 km, which is e = (r_a − r_p)/(r_a + r_p) = 177 / 84,331 ≈ 0.002. That tiny stretch makes the satellite slightly faster near its low point, which tilts and skews the eight a little.
A geostationary satellite is the limit i → 0, e → 0, where both swings vanish and the eight shrinks to a single point.
Every geostationary orbit is geosynchronous, because it has a one-day period. The reverse is not true: a geosynchronous orbit that is tilted or stretched makes the satellite move in the sky, so it is not geostationary.
Three are geostationary, at 32.5°E, 83°E and 129.5°E. Four are in geosynchronous orbits inclined 29°, two in each of two planes crossing the equator at 55°E and 111.75°E.
Up to 29° north and 29° south. The highest latitude of an orbit's ground track equals its inclination.