Crenation refers to the process of an object's shape or appearance becoming notched or serrated. The term is often used in botany, zoology or biology to describe an object such as a leaf, shell or cell that has lost water as a result of osmosis.
Typically, the concentration of solutes present inside of a plant or animal cell is in equilibrium with the external environment. Sometimes, via a process known as osmosis, a net movement of solvent occurs across a semipermeable membrane, such as the cell walls in a leaf or animal organ, to a region of higher solute concentration, in order to equalize the concentration of solutes on either side of the membrane. In some cases, this results in a solvent pressure that is greater outside of the membrane than inside of it. Commonly, this results in crenation, where cell membranes or the outer edges of a structure composed of many cells "shrivel", leaving a notched or serrated appearance.
An example of crenation is when the skin on a person's hands shrivels after prolonged suspension in saltwater. This happens because the greater concentration of salt in the saltwater environment draws water out of skin cells to equalize the concentration of salt inside and outside of the cells.