The movement of solvent from a region of its high concentration to a region of its low concentration through a semipermeable membrane is called osmosis.
During osmosis, the water molecules (solvent) are free to cross the plasma membrane in both the directions.
Osmosis is a passive process and happens without any expenditure of energy. It involves the movement of molecules from a region of higher concentration to lower concentration until the concentrations become equal on either side of the membrane.