Osmosis is the diffusion of water across a semipermeable membrane (usually cell membrane) from a region of low solute concentration to a more concentrated solution so it can reach equilibrium (balance).
Diffusion is a spontaneous movement of particles from an area of high concentration to an area of low concentration.
Both results in particles moving and help balance out the concentrations.
Also, in osmosis, the water molecules are moving. In diffusion, it is the solutes moving.
I hope this helps and explains well.