center of gravity
Definition from Wiktionary, the free dictionary
Alternative forms 
- (physics) a point, near or within a body, through which its weight can be assumed to act when considering forces on the body and its motion under gravity. This coincides with the center of mass in a uniform gravitational field
- (as a metaphor) any pivotal or central idea or group.
a point, near or within a body, at which the object's mass can be assumed to be concentrated