Simple Definition:

Revolution is a fundamental [big and important] and drastic [extreme] change in a system, organization, or society. It often involves the overthrow of a government [removal and replacement of the government by force] or a significant shift in power.

For example:

• The Industrial Revolution in the 18th century brought about major changes in manufacturing [making products] and transportation, leading to the rise of factories and steam-powered machines.
• The French Revolution in the late 18th century resulted in the overthrow of the monarchy and the establishment of a republic [a form of government where the power lies with the citizens].

Very Simple Definition:

Revolution is a big change that happens in a country or society. It can mean things become very different and people in charge can change.

For example:

• When people used to make things by hand, then changed to using machines, it was a revolution.
• When the leaders of a country are kicked out and new leaders take over, that is a revolution.