Osmosis is the diffusion of water across a membrane. Like other molecules, water will move from an area of high concentration to an area of low concentration. The more solute there is in a solution, the lower the concentration of water in that solution. There is terminology to describe concentration differences between two solutions. A solution with higher solute concentration is hypertonic relative to one with lower solute concentration. Conversely, a solution with lower solute concentration is hypotonic relative to one with higher solute concentration. If two solutions have the same concentration they are isotonic. Water will move from a hypotonic to a hypertonic solution.