This is the cavity of our organ. For example, it's the cavity of the stomach or it's the cavity of our small intestine. Now, the side of our cells that faces our lumen side is known as the apical side. But the other side that faces our basement membrane is known as the basil lateral side or simply the basal side. So we have this basal side that is attached to our basement membrane. And the basement membrane simply is a matrix that consists of specialized proteins and other molecules whose function is to basically act as a base for these cells.