Presidential System of Government
A system where a president is elected for a fixed, constitutionally prescribed term and in normal circumstances cannot be forced to resign by the legislature.
(Lijphart 1992, 3)
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Most such systems include the possibility of removing a president by the highly unusual and exceptional process of impeachment.
Reference
Lijphart, Arend, ed. 1992. Parliamentary versus Presidential Government. New York: Oxford University Press.