Newton,in 1687, discovered the existence of force between two masses.For example, two people sitting in room,a table and a rock lying in a room,sun and the earth.
The force between two masses is called GRAVITATION FORCE.The gravitational force is attractive.this is each body attracts towards it the other body.this force exists universally among all bodies in universe.
In gravitational force,we talk about the force of attraction between two bodies, out of these bodies, if one body is the earth, the gravitational force is called force of gravity.thus, the force of gravity is special case of the force of gravitation.
When a stone is released from the top of a tower, it falls towards the ground. Similarly, if a vody is thrown upward, its speed slows down.The speed becomes zero when the body reaches certain height.After the maximim height, the body begins falling down.Finally, the body returns to the ground.It implies that the earth attracts every body lying near its surface and on its surface towards its centre.The force of attraction of earth on the bodies lie on its surface is called gravity or force of gravity.
Not only earht but all the planets or heavenly bodies have gravity.the gravity of a body depends upon its mass.The gravity of moon is about 1\6th times the gravity of earth.