The gravitational constant, or G, is the universal constant of gravity, on Earth discovered by the Human scientist Sir Isaac Newton. It played a large role in his theory of universal gravitation, in the following formula:
where Fg is the gravitational force between two bodies, m1 is the mass of one body, m2 is the mass of the other body, and r is the distance between the centers of the two bodies.
In 2366, when Q temporarily became Human and hoped to join the crew of the USS Enterprise-D, Geordi La Forge and Data asked him to assist in preventing the moon of Bre'el IV from crashing into the planet. Q suggested changing the gravitational constant of the universe. Although this was beyond the capabilities of the Enterprise crew, it did lead to one possible solution: extending the ship's warp field around the moon, thus reducing the moon's gravitational constant. (TNG: "Deja Q")