Diffusion is defined as the movement of particles or molecules from a high concentration area to a low concentration area through uncoordinated movement.
Osmosis is a special type of Diffusion because it is the passing of water from a region of high concentration to a low concentration region through a semi-permeable membrane. It is a Physical process that is characterized by the movement of solvent without any energy applied, across a semi-permeable membrane that separates two solutions of varying concentrations.