To overturn means to flip something upside down or knock it over so it's no longer in its normal position. If you bump into a table and the glass of water on it falls and spills, you've overturned the glass. A strong wave might overturn a small boat, leaving it floating upside down in the water.

The word also describes reversing an official decision or ruling. When a higher court overturns a lower court's verdict, it declares that the original decision was wrong and shouldn't stand. A school principal might overturn a teacher's decision if new evidence shows a student was actually innocent of breaking a rule. Similarly, a government might overturn an old law that no longer makes sense.

Notice how both meanings share the idea of something being flipped from its original state: either physically turned upside down, or figuratively reversed from one decision to its opposite. When protesters work to overturn an unjust policy, they're trying to flip it completely, replacing it with something better. The word carries a sense of dramatic change: things don't just shift slightly when they're overturned; they end up in a completely different position than where they started.