A shadow is a dark area or shape produced when an object blocks light from a source, such as the sun or a lamp. Shadows can vary in size and shape depending on the angle and intensity of the light, as well as the object's form. Shadows are commonly seen on the ground or on surfaces behind the object. They can change throughout the day as the position of the sun moves across the sky, creating longer or shorter shadows. Shadows are also used in art and photography to create depth and contrast.