The movement of particles from a region of higher concentration to a region of lower concentration through a semi permeable membrane is called osmosis. The direction and rate of osmosis depend on the pressure gradient and concentration gradient.
The osmotic pressure can be defined as the actual hydrostatic pressure (pressure related to water) which develops in a solution due to the presence of dissolved solutes when it is separated from pure water by means of a semipermeable membrane.
The magnitude of the osmotic pressure is a function of solute concentration in a solution. It is higher in the case of xerophytes as compared to mesophytes while mesophytes have higher osmotic pressure than hydrophytes. It is also noted that an isolated solution without solute, and not bounded by any membrane, has no osmotic pressure. This negative osmotic pressure is called osmotic potential. For the development of osmotic pressure a confined space is required.
Numerically osmotic pressure is equivalent to the osmotic potential, but the sign is opposite. Osmotic pressure is the positive pressure applied, while osmotic potential is negative. Example the function of solute concentration in a solution is the magnitude of osmotic potential. Such a solution has an osmotic potential which is a negative of osmotic pressure.