Answer: Presidential Democracies have their power being held by the People, while Constitutional Monarchies usually incorporate power by sharing it with accordance to the People.
Explanation: The United States is considered a Presidential Democracy. Unlike the United Kingdom, it doesn't have a Head of a Certain Family representing the Government or the State. The United Kingdom does, with it's royal family, the House of Windsor, which presents it as a Constitutional Monarchy as it doesn't give up it's power with the populace.