A specialization of axisymmetric object (q.v.). Each instance of bilaterally symmetric object is a (tangible or intangible) spatial object that is symmetric with respect to some bisecting straight line (if the object is planar) or plane (if it's non-planar). In this context, symmetric means that the line or plane divides the object into two equal halves with the same shape (or mirror-image shapes). For example, a circle, an isosceles triangle, a cone, and a human body are all bilaterally symmetric objects.

If a bilaterally symmetric object OBJ is a one- or two-dimensional planar region, then any bisecting line with respect to which OBJ is symmetric is an axis of symmetry (see Symmetric Axes) of OBJ. If OBJ is a two- or three-dimensional non-planar object that is symmetric with respect to a bisecting plane PLANE, then any straight line with respect to which the space-region intersection of OBJ and PLANE is symmetric is itself an axis of symmetry of OBJ. Thus, a circle has an infinite number of axes of symmetry (viz. any straight line that intersects the circle and passes through its center); an isosceles triangle has exactly one axis of symmetry; a cone has at least one axis of symmetry; and a human body has no axis of symmetry (though it does have three Object Axes (q.v.)).

See also radial thing.