Definition:Bilateral Symmetry

Definition

Let $F$ be a geometric figure.

Let there exists a reflection $R$ in the such that $\map R F$ is a symmetry.

Then $F$ has bilateral symmetry.

Axis of Symmetry

Let $F$ be a plane geometric figure.

Let $\map R F$ be a reflection in an axis of reflection $AB$ which is a symmetry.

Then $AB$ is referred to as an axis of symmetry of $F$.

Linguistic Note

The word bilateral derives from the Latin bis (meaning ‎twice) and laterālis (meaning pertaining to the side).

It literally translates as two-sided.