Any massive object creates a gravitational field around it.
On the surface of a spherical massive object, like the earth or the sun, there is a gravitational acceleration associated with this gravity. When you throw a ball up into the air with some velocity, this gravitational acceleration forces the ball to drop back to the surface of the earth. However, if you give the ball or any object enough velocity, it will be able to escape the gravitational field of the massive object. This minimum velocity needed to escape the gravitation acceleration is the massive object s escape velocity. If it is traveling any slower, it will be forced to fall back to the surface of the earth.