The word revolution has two major meanings:

1. A complete change that transforms how things work or how people think. The Industrial Revolution changed how people made goods, moving work from homes and small shops to large factories powered by machines. The invention of the printing press sparked a revolution in how knowledge spread. When scientists develop a revolutionary new treatment for disease, they're creating something that fundamentally changes medicine. Revolutionary changes don't just improve things slightly: they remake them entirely.
2. When people overthrow their government and replace it with a new system. The American Revolution happened when the thirteen colonies fought to become independent from British rule. The French Revolution overturned the monarchy and established a republic. Revolutions usually happen when many people believe their government is unjust or that they lack basic freedoms and rights. They're dramatic upheavals that reshape a nation's political system.

Think of a wheel making one complete revolution as it turns. That image of something turning completely around captures both meanings: society rotating to an entirely new position, or power revolving from one group to another.