center of gravity
1. Abbr. cgThe point in or near a body at which the gravitational potential energy of the body is equal to that of a single particle of the same mass located at that point and through which the resultant of the gravitational forces on the component particles of the body acts.
2. The point of greatest importance, interest, or activity:
“The center of gravity for the English language is no longer Britain. American English is the greatest influence on English everywhere”(Robert W Burchfield)