A plane of symmetry of a geometric object in three-dimensional space, such as a surface or solid, is a plane such that reflection in the plane maps the object onto itself. Equivalently, it divides the object into two parts that are mirror images.
A right circular cylinder has infinitely many planes of symmetry containing its axis of symmetry, as well as the plane midway between its bases. A right circular cone has infinitely many planes of symmetry containing its axis of symmetry, and every plane through the center of a sphere is a plane of symmetry.
