A constitution is a set of fundamental rules and principles that establishes how a government works and what powers it has. Think of it as an instruction manual for running a country: it explains who makes the laws, who enforces them, who judges disputes, and what rights the citizens have that the government cannot take away.

The United States Constitution, written in 1787, is one of the most famous constitutions in the world. It created three branches of government (legislative, executive, and judicial) to prevent any single person or group from having too much power. It also includes the Bill of Rights, which guarantees freedoms like speech, religion, and assembly.

Most countries have written constitutions that are single documents you can read and study. Britain famously has an “unwritten constitution” made up of many laws, court decisions, and traditions built up over centuries. Either way, a constitution serves as the highest law of the land: regular laws must follow what the constitution allows, or courts can strike them down as unconstitutional.

The word can also mean the physical makeup or health of something. A person with a strong constitution rarely gets sick and bounces back quickly from illness. A building with a sturdy structure withstands storms and earthquakes. This meaning captures the idea of a basic framework, whether for a government or a person's body.