Define gravity and also define gravitional …

Gravitation is the attractive force existing between any two objects that have mass. The force of gravitation pulls objects together.

Gravity is the gravitational force that occurs between the earth and other bodies. Gravity is the force acting to pull objects toward the earth. 

Since gravitational force is happening to all matter (objects) in the universe, from the largest galaxies down to the smallest atoms, it is often called universal gravitation. Sir Isaac Newton was the first to fully recognize that the force holding any object to the earth is the same as the force holding the moon, the planets, and other heavenly bodies in their orbits. According to Newton 's law of universal gravitation any two masses in the universe attract each other with a gravitational pull. The size of this force is given by 

f=gmM/r²

where
f is force
g is acceleration due to gravity
m and M are masses of the bodies.
r is distance between the bodies or radius of the body accordingly.