Answer:
A government, whichever it may be, is generally defined as a group of people who have the power, or authority to govern a nation, or a state. This power to govern may derive, as it is today, from the election and acceptance of such power by the people who are governed (as is the case of presidents or prime ministers in the world), or from some form of repression (as is the case of totalitarian governments, or tyrannical rules).
In the United States, government comes from the authority given to a group of elected officials, who will represent the people who has elected them in one of the three main branches of power: the executive, the legislative and the judiciary.
From the very beginning of the U.S as a country, and given their rejection towards what a totalitarian government (like the rule of the King of England) entailed, they adopted the constitutional principle of the separation of powers, meaning, the creation of three separate, unique, and equally powerful branches of government, whose role was not just to lead, but to ensure the balance between them. It was also established that their officials would be elected by the people, thus their power came from the people.
This would be, in general the definition of both what a government is, what the U.S government is and how the Separation of Powers, also known as the check and balances principle, works.
