Noun, pl. cell walls
1. A membrane of the cell that forms external to the cell membrane whose main role is to give cells rigidity, strength and protection against mechanical stress. It is found in cells of plants, bacteria, archaea, fungi, and algae. Animals and most protists do not have cell walls. (biology-online.org)
2. (Cytology)
A thick, fairly rigid, layer formed around individual cells of bacteria, Archaea, fungi, plants, and algae (but not animals and other protists which generally have cell membranes without cell walls). The cell wall is external to the cell membrane and serves a structural function helping the cell maintain its shape and protecting the cell from damage. (Wiktionary.com)
3. The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, in addition to acting as a filtering mechanism. (Wikipedia.com)
4. The outermost layer of a Cell in most Plants; Bacteria; Fungi; and ALGAE. The Cell wall is usually a rigid structure that lies external to the Cell Membrane, and provides a protective barrier against physical or chemical agents. (online-medical-dictionary.org)