The LEO orbit (Low Earth Orbit) is a circular orbit between 500 and 2000 km altitude. The close proximity of the orbit has two advantages: a very short latency time (the time the signal takes to arrive) and a reduced power requirement to establish contact.
The period of a satellite is of the order of a few hundred of minutes. As the orbit is low, the velocity must be very high to counter the attraction of the Earth. A satellite goes round the Earth about 14 times a day and its coverage varies between 3000 and 4000 km: a terrestrial observer can only see the satellite for about 20 minutes. This type of satellite is also called a moving satellite.