Osmosis

 So you put salted water in a 'U' shapes tube, and put a semi-permeable membrane in the middle of that tube. Now there are two parts inside the tube, separated by a semi-permeable membrane. You put a turbine in the part where the water is more concentrated with salt. The pressure changes, moves the water, and that spin the turbine enough to spin the magnet of a generator.
This, is one of the things you can call osmosis.

Osmosis is a type of diffusion. Osmosis can occur when there is a partially permeable membrane, such as a cell membrane.
When a cell is submerged in water, the water molecules pass through the cell membrane from an area of low solute concentration to high solute concentration (e.g. if the cell is submerged in saltwater, water molecules move out; if it is submerged in freshwater, however, water molecules move in); this is called osmosis. This happens, because the setup is trying to 'even out' the concentration of salt inside the tube, maintaining an equilibrium.
This is, what I think is called; Osmosis.