They are the three main height bands for Earth satellites: low Earth orbit up to 2,000 km, geostationary orbit at 35,786 km, and medium Earth orbit in between.
Satellites are sorted by how high they fly, because height decides how fast a satellite moves, how long one lap takes and how much of Earth it can see at once.
Low Earth orbit (LEO) starts just above the atmosphere and runs up to 2,000 km. Geostationary orbit (GEO) is one exact height: 35,786 km above the equator. Medium Earth orbit (MEO) is the wide band between the two.
Satellites in LEO move at about 7.8 km/s and go round Earth in about 90 minutes. Below about 180 km the air is thick enough to slow them down quickly, so satellites are rarely placed lower than that.
India's Cartosat-3 mapping satellite is a LEO satellite. It flies at a mean altitude of 509 km, close enough for its camera to pick out features about 25 cm across. The price of being close is that it sees only a narrow strip of ground at a time.
GPS satellites fly about 20,200 km up and take 12 hours per orbit. Europe's Galileo navigation satellites also use MEO.
India chose a different layout for NavIC. Its seven satellites sit at geosynchronous height instead: three in geostationary orbit and four in geosynchronous orbits tilted 29° to the equator. That keeps all of them over the Indian region, which is the area NavIC is built to serve.
For a circular orbit the speed is v = √(GM/r), where GM for Earth is 398,600 km³/s² and r is the distance from Earth's centre (height + 6,378 km).
Cartosat-3 is a low Earth orbit satellite: watch its estimated position sweep across the globe and complete a full lap in about 95 minutes. Track Cartosat-3
A circular orbit needs gravity to supply exactly the centripetal force: GMm/r² = mv²/r, so v = √(GM/r). The period is the circumference divided by the speed: T = 2πr/v = 2π√(r³/GM). This is Kepler's third law for a circular orbit: T² ∝ r³.
With GM = 398,600 km³/s² and Earth's equatorial radius 6,378.137 km (NASA Earth Fact Sheet):
Note the pattern: going from 509 km to GEO multiplies r by about 6.1, so the speed falls by √6.1 ≈ 2.5 times and the period grows by 6.1^1.5 ≈ 15 times. Higher satellites are slower and their laps are much longer.
Medium Earth orbit, about 20,200 km up. Each satellite takes about 12 hours to go round Earth once.
The atmosphere there is dense enough to slow them down quickly, so their orbits would decay within a short time.
The 509 km satellite. Using v = √(GM/r), it moves at about 7.6 km/s against about 3.1 km/s for the geostationary one — roughly 2.5 times faster.