A constitutional democratic republic is a type of government based on the principles of a constitution in which officials elected by the people represent the people in the legislative and governing processes. A constitutional republic is not a direct democracy in that a mere plurality of the voters does not get to control the processes of the government directly.
The United States is an example of a constitutional democratic republic. The government is run according to the principles of an established Constitution, and the people do not pass laws based on a direct majority. Rather, they elect representatives to a legislative body who can then represent their interests but who can only pass laws that adhere to the principles of the Constitution.
One of the main principles of the U.S. Constitution is the division of powers among the three parts of the government, the executive, legislative, and judicial branches, through a system of checks and balances. The executive branch has the power to veto laws passed by the legislative branch that it deems unconstitutional. If challenged by the people, the judicial branch has the power to strike down laws it considers unconstitutional. The legislative branch, however, retains the powers to revise such laws so that it meets the constitutional benchmarks as expressed by other branches, and it also retains the important power of passing new laws.