Contrast is the dissimilarity or difference between things, objects, colors. Constrast single out what we want to show on our image gave us specific compound view. We see contrast everywhere, in every aspect of our life. Creating work we single out object or effects specially by abusing it, contrast light to shadow, contrast by color or just structure or sense the objects.
Example of what light could show from the shadow.
Example of what color could do in image.
Example of different sense objects.