A constitutional republic is a state in which the head of state and other officials are representatives of the people and must govern within an existing constitution. In a constitutional republic, executive, legislative, and judicial powers are separated into distinct branches.
A federal republic is a federation of states with a republican form of government. At its core, the literal meaning of the word republic when used to reference a form of government means: "a country that is governed by elected representatives and by an elected leader (such as a president) rather than by a king or queen".
A parliamentary system is a system of democratic governance of a state where the executive branch derives its democratic legitimacy from its ability to command the confidence of the legislative branch, typically a parliament, and is also held accountable to that parliament.
A presidential system is a democratic and republican system of government where a head of government leads an executive branch that is separate from the legislative branch. This head of government is in most cases also the head of state, which is called president.
How Is Representative Democracy Defined? Simply put, a representative democracy is a system of government in which all eligible citizens vote on representatives to pass laws for them. A perfect example is the U.S., where we elect a president and members of the Congress. We also elect local and state officials.
If the head of state of a republic is also the head of government, this is called a presidential system. There are a number of forms of presidential government. A full-presidential system has a president with substantial authority and a central political role.
A unitary state refers to a country that has one supreme authority which rules over all other delegations. A unitary state is the opposite of a federation where powers are dispersed. A unitary state only exercises the powers that the central government decides to delegate.