Osmosis
Osmosis is the special case of diffusion involving water molecules. Water molecules move from areas of high water concentration to areas of low water concentration through a selectively permeable membrane.
A selectively permeable membrane allows small, soluble molecules to pass through it, but prevents large insoluble molecules from passing through.
Osmosis is the movement of water molecules through a selectively permeable membrane from higher water concentration to a lower water concentration - or - down a concentration gradient.