The Collaborative International Dictionary
osmotic pressure \os*mot"ic pres"sure\, n. (Physical Chemistry) The pressure which a solution of a substance in a liquid exerts on a semipermeable membrane, through which the solvent can diffuse but the dissolved substance (the solute) cannot diffuse, when separated across the membrane from the pure solvent. In general, the osmotic pressure will depend almost proportionally up to certain concentrations upon the molal concentration of the solute.
Wiktionary
n. (context physics English) The hydrostatic pressure exerted by a solution across a semipermeable membrane from a pure solvent; the pressure needed to counteract osmosis
WordNet
n. (physical chemistry) the pressure exerted by a solution necessary to prevent osmosis into that solution when it is separated from the pure solvent by a semipermeable membrane
Wikipedia
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. It is also defined as the measure of the tendency of a solution to take in water by osmosis. Potential osmotic pressure is the maximum osmotic pressure that could develop in a solution if it were separated from distilled water by a selectively permeable membrane. The phenomenon of osmosis arises from the propensity of a pure solvent to move through a semi-permeable membrane and into a solution containing a solute to which the membrane is impermeable. This process is of vital importance in biology as the cell's membrane is semipermeable.
Usage examples of "osmotic pressure".
By employing dilute alcohol, the mobility of the inorganic ions is restricted and the osmotic pressure raised-a desirable effect, of course.
Since they evolved on such a hot planet, they have a water-regulating physiology, reacting to osmotic pressure.
Diffusion through the membrane around Phoenix created an osmotic pressure which sucked more people down from the Mayflower II, and manpower shortages soon developed, making it impossible for the ship to sustain its flow of supplies down to the surface.
So there was a good deal of membrane damage through osmotic pressure.