Osmotic pressure
Osmotic pressure is an outward force/pressure developed when a solution takes up water.
A solution has a tendency to take up water across a semi-permeable membrane. The pressure developed when such a solution takes up water by osmosis is called osmotic pressure. A more concentrated solution will exert a greater osmotic pressure.
Osmotic potential
Osmotic potential is the ability of water molecules to diffuse out of a solution.
Every solution has a water potential. The more dilute a solution is the higher the water potential. Water will move from a region of high water potential (dilute solution) to a region of low water potential (concentrated solution).
The ability of water molecules to diffuse out of a solution is called osmotic potential. Pure water has the greatest osmotic potential.