A republic is not necessarily a democracy, and the two terms are not strictly interchangable. A republic may take many forms, including but not limited to democratic, mercantile, classical, and religious republics.
Constitutionally the USA is a representative democracy defined as republican in modern political argot. If you have the time a reading of Federalist No. 10 is quite enlightening (although a little tough).
Constitutionally the USA is a representative democracy defined as republican in modern political argot. If you have the time a reading of Federalist No. 10 is quite enlightening (although a little tough).