OsmosisOsmosis is the passive movement of water through a semipermeable membrane from a compartment of relatively low osmotic pressure to a compartment of relatively high osmotic pressure, toward equilibrium.  A semipermeable membrane, as it is used here, is defined as a membrane that is permeable to water, but impermeable to certain solutes.  The osmotic pressure responsible for osmosis is generated by these impermeable solutes.  The greater the concentration of impermeable solutes, the greater the osmotic pressure.