Definition of CELL WALL for Kids. : the firm outer nonliving layer that surrounds the cell membrane and encloses and supports the cells of most plants, bacteria, and fungi. noun.efinition of CELL WALL. : the usually rigid nonliving permeable wall that surrounds the plasma membrane and encloses and supports the cells of most plants, bacteria, fungi, and algae — see cell illustration. See cell wall defined for kids. ADVERTISEMENT.