Theory:

Symmetry is everywhere. It is present in both natural and artificial bodies. Natural bodies might include leaves, butterflies and so on, whereas artificial bodies might consist of human-made constructions.
 
1.png  shutterstock_1164747724.jpg
An object is said to be symmetrical when you cut the thing into two and both the halves look identical. The two symmetrical halves are like a mirror image, and they complete each other.
2(1) Ресурс 1.png
The line that dissects the image into two halves is called the line of symmetry or the axis of symmetry.
There can also be two or more lines of symmetry.
 
The lines that do not dissect the images into two identical halves are not considered as lines of symmetry.