Geometry. the middle point, as the point within a circle or sphere equally distant from all points of the circumference or surface, or the point within a regular polygon equally distant from the vertices.
a point, pivot, axis, etc., around which anything rotates or revolves: The sun is the center of the solar system.
the source of an influence, action, force, etc.: the center of a problem.
a point, place, person, etc., upon which interest, emotion, etc., focuses: His family is the center of his life.
a principal point, place, or object: a shipping center.