Let 
be a 
-dimensional
vector space over 
, let 
, and let
 |
be a subspace of 
of dimension 
, where 
is a unit normal
vector of 
.
Then 
is said to have mirror symmetry about 
if 
contains the vector
 |
whenever it contains 
.
The vector 
is the mirror image of 
about 
. For a plane figure, 
and the subspace 
is a line called an axis
of symmetry. For a geometric object in three-dimensional space, such as a surface or solid, 
and 
is a plane of symmetry.
Mirror symmetry is sometimes called bilateral symmetry. Most animals are very nearly bilaterally symmetric. Molecules without bilateral symmetry come in two varieties denoted L (laevo) and R (dextro), each of which is the mirror image of the other. Such images are called enantiomers, and their property of being the same except by reflection is called handedness. Some highly symmetric geometric solids, including the snub cube and snub dodecahedron, also lack mirror symmetry and come in two enantiomorphous forms.
