A parliamentary republic is a republic that operates under a parliamentary system of government where the executive branch (the government) derives its legitimacy from and is accountable to the legislature (the parliament). There are a number of variations of parliamentary republics. Most have a clear differentiation between the head of government and the head of state, with the head of government holding real power, such as in constitutional monarchies. However, in some countries the head of state has 'reserve powers' to use at their discretion as a non-partisan 'referee' of the political process. Some have combined the roles of head of state and head of government, much like presidential systems, but with a dependency upon parliamentary power.