Osmosis is the natural movement of water through a thin barrier from an area where there's more water to an area where there's less water. Think of a sponge sitting in a puddle: the water moves into the sponge without anyone squeezing or forcing it, because that's where water naturally wants to go.

This happens constantly in living things. When you water a plant, osmosis moves water from the soil through the plant's roots and up into its leaves. Inside your own body, osmosis helps water move in and out of your cells, keeping them healthy and properly hydrated.

Scientists study osmosis because it's essential for understanding how living things work. The process happens through what's called a semipermeable membrane, a barrier that lets water pass through but blocks other substances.

People also use osmosis loosely to mean learning something without much effort, as if knowledge just soaks into your brain. You might joke that you're learning Spanish by osmosis from sitting near students who speak it, but real learning still requires actual study and practice.