The dividing point that creates symmetry is called the line of symmetry or the line of reflection. Objects on both sides of the line of symmetry will be exactly the same, appearing as mirror objects of each other. Lines of symmetry can be horizontal, vertical or diagonal.
When an object is divided by a line of symmetry and the two resulting halves are identical, they are congruent or matching. When an object has multiple lines of symmetry, it will have multiple congruent parts.
Objects can have multiple lines of symmetry, running in different directions simultaneously. This is seen in flowers, snowflakes and man-made rugs. When this occurs, the points of symmetry intersect in the center of the object.
Asymmetry occurs when a dividing line does not pass through the center of an object, even if the object is evenly proportioned, resulting in disproportionate objects on each side of the dividing line. Symmetry also cannot occur in irregularly-shaped objects; these objects are also referred to as asymmetrical even though they do not have a line of symmetry at all.