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The term low Earth orbit (LEO) indicates orbits closest to the Earth, specified as having an orbital period of no more than 128 minutes, stretching no more than about 2000 km from the Earth's surface. This includes the majority of Earth satellites for communications, surveillance, and research, currently on the order of 2000, with current plans for many more. It includes some astronomy satellites, such as the Hubble Space Telescope (HST).
Such orbits are the most economical to launch to and are below the Van Allen belts (orbits within the belts are dangerous to humans and equipment, and orbits below them are somewhat protected from dangerous particles), but are subject to orbital decay from atmospheric drag. The only manned space-flights to go beyond low Earth orbits have been the Apollo Moon missions.
Alternatives to LEOs are orbits further from Earth, which include as Mid Earth orbits (MEOs), geosynchronous orbits (GEOs, that have an orbital period of exactly one Earth day), Solar orbits, and orbits of Earth-Sun Lagrangian points (commonly used for astronomy).
Also, Leo is a well-known constellation, used in the designations of galaxies, etc., such as Leo A.