All substances have a tendency to undergo diffusion.
In diffusion, the random movement of individual molecules results in a mass movement from regions of high concentration to regions of lower concentration. For example, if you open a bottle of perfume indoors, the odor molecules gradually diffuse outward from the bottle to spread throughout the room. The perfume would eventually stop diffusing when the concentrations are equal in all parts of the room. Water, like any other substance, can also undergo diffusion, and in the case of water this is referred to as osmosis. To understand how osmosis works, it helps to think of the individual water molecules.