What do you mean by Osmosis?

Osmosis is a process of a cell by which it releases water or takes water from the outside environment of cell.

Diffusion is a movement of particles from an area of high concentration to an area of low concentration whereas, osmosis is a special type of diffusion by which water moves from its higher concentration when two concentrations are separated by a semipermeable membrane or deferentially permeable membrane. Osmosis process is seen when red blood cell (RBC) is placed into fresh water. The membrane of RBC is semipermeable, it takes up water and swells.