Symmetry - Symmetry refers to visual elements mirrored to the other half of the surface or form, in the case of 3-dimensional objects. Symmetry requires an axis by which the mirroring occurs. This axis can be vertical (left-right mirroring), horizontal (top-bottom mirroring), or diagonal.
Rotational symmetry refers to a variation in symmetry that allows for more than one mirroring of visual elements around a central point, rather than an axis. A kaleidoscope is an example of rotational symmetry.
Symmetry (vertical axis)
Symmetry in architecture: reconstruction of the Parthenon (vetical axis)
Claude Monet. Misty Morning on the Seine, Mauve. 1897.
Symmetry (horizontal axis)
Radial Symmetry (horizontal and veritcal axis)