Water potential is the difference in the potential energy of water per unit volume from that of pure water. It is a measure of the tendency of these molecules to diffuse to another area. The more free water molecules, the higher the water potential.
Water diffuses by osmosis from a region of high water potential to a region of low water potential through the water potential gradient. Osmosis can therefore be defined as the diffusion of water from a region of high water potential to a region of low water potential through a partially permeable membrane.