Definition of seperation of powers

It means that the governmental power of the United States is divided, or "Separated", into 3 branches- the Executive (the president), Legislative (the congress), and Judicial (the Supreme Court). The separation of powers was to ensure that no one branch of the government became too dominant. (Note that "Separation of Powers" does not only apply to the United States; some other democracies have similar ways of making sure there are checks and balances on the power of the country's leaders.)