When light falls on a surface, the direction of the ray is changed. This change in direction is known as reflection of light. e.g. you see your reflection in a pool of water or mirror. While
Shadow is an image formed by obstruction of light e.g. if you place your hand in front of a candle or torch, you will see the image of the hand on the wall. This image will only show the outline of the object placed in front of the light source.