And that's because our hand, the impermeable barrier, actually creates a pressure that prevents that osmosis from taking place. And that's exactly what osmotic pressure is. Osmotic pressure is the pressure that needs to be applied to actually prevent osmosis from actually taking place. So if we block the semipermeable membrane with some type of impermeable barrier, for example, our hand, we will be applying a pressure that will ultimately stop osmosis from taking place. So the pressure that must be applied to stop the natural flow of water down its osmotic potential gradient is called osmotic pressure. So notice that the water tries to move this way, but our osmotic pressure points in the opposite direction because what it does is it ultimately stops the water from actually moving across this membrane.