Learner's definition of SPHERE
1 a : a round object b geometry : a three-dimensional shape that looks like a ball 2 somewhat formal : an area of influence or activity
Women at that time were confined to the domestic sphere.
They recognize that jobs in the public/private sphere are valuable.
The region has moved back and forth between Spanish and Portuguese spheres of influence. [=has been under the control or influence of Spain and Portugal at different times]