Osmosis

Osmosis is the diffusion of water molecules from an area of high water potential (dilute solution/high concentration of water) to an area of low water potential (concentrated solution/low concentration of water) through a partially permeable membrane.

A partially permeable membrane is one that allows small molecules (like water) through, but not larger molecules (like solute molecules).

In a hypertonic solution (a highly concentrated solution), cells will shrivel