TechnicalGTO
Geostationary Transfer Orbit
A highly elliptical orbit used to move a spacecraft from low altitude up to the geostationary belt, where it then circularises.
A geostationary transfer orbit is an elliptical orbit with a perigee near low Earth orbit altitude and an apogee at or near geostationary altitude. Launch vehicles often deliver payloads to GTO, after which the spacecraft uses its own propulsion to circularise at GEO.
GTO operations and the disposal of spent upper stages left in such orbits are relevant to debris mitigation, because these high-energy orbits cross many altitudes.