1. (cell coat) A layer of carbohydrate on the surface of the plasma membrane of most eukaryotic cells. It is made up of the oligosaccharide side-chains of the glycolipid and glycoprotein components of the membrane and may include oligosaccharides secreted by the cell. It plays a role in cell-cell adhesion and in regulating the exchange of materials between a cell and its environment.

2. The outermost layer of a bacterium, typically consisting of numerous polysaccharides plus various glycoproteins. The glycocalyx varies in thickness and consistency: in some species it forms a flexible slime layer while in others it forms a rigid and relatively impermeable capsule.