Definition: OSMOSIS is the movement of water molecules across a partially permeable membrane from a region of high water concentration (*dilute) to a region of low water concentration (*concentrated)
*To remember this, relate it to squash. When you have squash with little or no water in it, it is concentrated but when when you put water in it, it becomes dilute. Therefore concentrated means less water and dilute means more water.
Also if the definition seems complicated to you, remember that it is just a type of diffusion but of only water molecules.