The answer is a republic.
Direct democracy is where the majority people themselves decide on policies directly. America has a form of government that has a representative group of people who are elected by the majority, and they decide on policy.
A Monarchy is a form of governance where a single person is in charge of policy. Usually this person is born into the role of leader of their people. Think King and/ or queen.
An autocracy is a system of government in which an autocrat, a single person, or a party that possesses supreme power. this could be a dictator or a political party. This also could fall under monarchy, somebody who has been born into the position of ruling the government.
A republic is a state in which supreme power is held by the people and the people elect representatives.
America‘s form of governance is a constitutional federal republic.
I hope that helps.