Osmosis
The net movement of solvent molecules through a semipermeable membrane from a dilute to a concentrated solution.
Unit
Dimensionless
In depth
The membrane passes solvent but blocks solute, so solvent flows in the direction that dilutes the concentrated side and equalises chemical potential. Osmosis is the mechanism by which plant roots take up water and by which cells maintain their volume and turgor.
Examples in the real world
A raisin swelling in water; red blood cells bursting when placed in distilled water.