Diffusion and osmosis are both examples of transport phenomena. In other words, particles are transported from one area to another without a net infusion of energy or mechanical intervention. The difference between the two is what is transported and through what medium. Diffusion is the movement of solute particles in a given solution from an area of high concentration to an area of low concentration. The solute particles ultimately spread themselves evenly throughout the solvent to form a uniform concentration. Osmosis is the movement of solvent particles through a semipermeable membrane to even out any concentration gradient on both sides of the membrane. So the key differences between the two are that diffusion involves movement of solute particles while osmosis involves movement of solvent particles and osmosis involves a semipermeable membrane while diffusion does not.