difference

Diffusion is the spontaneous movement of a substance from a region of its higher concentration to a region of its lower concentration. Osmosis is diffusion followed by water molecules. Here, water molecules move from a region of higher water concentration through a semi-permeable to a region of low water concentration.

Diffusion occurs without a membrane whereas osmosis occurs across a semi-permeable membrane.

Diffusion may also occur in gases besides liquids, but osmosis only occurs in aqueous solutions.

Osmosis is also relatively slower than diffusion.

Diffusion may disperse molecules over a very long distance but osmosis generally occurs over a short distance.