A prime minister, premier or chief of cabinet is the head of the cabinet and the leader of the ministers in the executive branch of government, often in a parliamentary or semi-presidential system. Under those systems, a prime minister is not the head of state, but rather the head of government, serving as the principle administrator under either a monarch in a monarchy or a president in a republican form of government.
In parliamentary systems fashioned after the Westminster system, the prime minister is the presiding and actual head of government and head/owner of the executive power. In such systems, the head of state or their official representative (e.g., monarch, president, governor-general) usually holds a largely ceremonial position, although often with reserve powers.
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