Question

What is osmotic pressure?

Answer 1

The pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution.

Answer 2

Osmotic Pressure is the amount of pressure required to stop entry of water into a solution across semipermeable membrane, is called osmotic pressure.  It is the function of solute concentration, more the solute concentration greater will be the pressure required to prevent water from diffusing in. Numerically osmotic pressure is equivalent to solute (osmotic) potential but sign is opposite.  Osmotic pressure is positive while osmotic potential is negative.