When you throw a stone upwards, the stone returns to the ground after reaching some height due to gravitational force of earth.

 But, if you keep on increasing the speed at which you through the stone, then there comes a time when the stone will not return back to Earth. This special speed is called Escape Velocity with respect to Earth.

Escape velocity is the speed that an object needs to be traveling to break free of a planet or moon’s gravity and leave it without further propulsion. Escape velocity on Earth is 11.2 km/second.