The term 'GROUND LAYER' can be summarized as a layer of soil or turf that is laid down on the ground. The most common type of ground layer is known as SOD, which is a three-letter word. SOD is a grassy surface made up of soil and grass that is cut into small pieces and then laid down on the ground. It is often used to create a lawn or to cover bare patches of land. SOD is also used to help prevent erosion and to improve the appearance of a landscape.