Newton's law of gravitation states that every particle attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
The symbol G is Newton's universal law of gravitation in the gravitational force between two objects is proportional to the mass of each and inversely proportional to the square of the distance between them
It is called so because it is applicable on all bodies having mass, and the bodies will be governed by the same law, that is newton's law of gravitation. Thus, as it is applicable universally, it is called as universal law.