Low Earth Orbit (LEO) refers to a satellite which orbits the earth at altitudes between (very roughly) 200 miles and 930 miles.
Low Earth Orbit satellites must travel very quickly to resist the pull of gravity — approximately 17,000 miles per hour. Because of this, Lowe Earth Orbit satellies can orbit the planet in as little as 90 minutes.
Low Earth Orbit satellite systems require several dozen satellites to provide coverage of the entire planet.
Low Earth Orbit satellites typically operate in polar orbits.
Low Earth Orbit satellites have a typical service life expectancy of five to seven years.