cen'ter of grav'ity
1. Mech.the point through which the resultant of gravitational forces on a body passes and from which the resultant force of attraction of the body on other bodies emanates: coincident with the center of mass in a uniform gravitational field.
2. a person, thing, or idea that is the vital or pivotal focus of interest or activity within a larger entity.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.