A geostationary satellite is called so because it appears to be stationary when observed from any location of the earth. This happens when the time period of the satellite is equal to the rotational period of the earth i.e. 24 hours. Also, the direction of motion of the satellite must be same as that of the earth and the satellite should be at a height of about 36000 km.
Home Gravitation Reasonings Why is a geostationary satellite called so?