Osmosis is defined as the process in which the flow of water takes place from the higher concentration region to a low concentration region across a semi-permeable membrane. Osmosis helps in equalising the concentration of water on either side of the membrane. It is also considered to be a passive transport as there is no requirement of energy.
Osmosis is a special kind of diffusion because in both cases there is a movement of particles from a higher concentration region to a lower concentration region. The only difference is that osmosis is applicable to the movement of the solvent only through the semi-permeable membrane where the solvent is water.