pressure generated by the movement of water across the cell membrane caused by the difference between solute concentrations on each side.

Merriam-Webster Online Dictionary
osmotic pressure (noun)
the pressure produced by or associated with osmosis and dependent on molar concentration and absolute temperature as
a) the maximum pressure that develops in a solution separated from a solvent by a membrane permeable only to the solvent
b) the pressure that must be applied to a solution to just prevent osmosis
osmotic pressure (Wikipedia)

Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is also defined as the measure of the tendency of a solution to take in its pure solvent by osmosis. Potential osmotic pressure is the maximum osmotic pressure that could develop in a solution if it were separated from its pure solvent by a semipermeable membrane.

Progression: (1) a U-tube is filled with water and has a membrane in the middle (2) sugar is added to the left part (3) water crosses the membrane and fills the left side more than the right.
Osmosis in a U-shaped tube

Osmosis occurs when two solutions containing different concentrations of solute are separated by a selectively permeable membrane. Solvent molecules pass preferentially through the membrane from the low-concentration solution to the solution with higher solute concentration. The transfer of solvent molecules will continue until equilibrium is attained.

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