Definition:Symmetry


 * Symmetry (of a relation): whether a relation is symmetric, antsymmetric, asymmetric or non-symmetric.
 * Symmetry mapping: A movement of a geometric figure so that it looks the same after it has been moved.
 * Symmetry group: The set of all symmetry mappings of a geometric figure, the operation being composition of mappings.

Linguistic Note
The word symmetry comes from Greek συμμετρεῖν (symmetría) meaning measure together.