A republic is a representative form of a democracy. What sets apart a republic from a true democracy is that in a republic leaders are elected and those leaders actually handle the day to day decision making of the government. In a pure democracy the people hold a forum to decide nearly every issue. A republic can take many forms and how the members of the ruling body are selected vary from one to another. A example of a republic from ancient days is the Pre-Empire Roman Republic.
In science fiction, "republic" may refer to:
There is the Roman Republic that was lead by the usually appointment designated Senate as the major ruling body of the system. One of the best modern examples is the United States of America still currently in operation.
The Republic system under the United States.
The Rules of the Republic that is the United States of America, are laid out by the Constitution of the United States. Before the framing of this system the country was ruled by a very simplified version of what was very similar to the Roman system with only one vote per member state. Under the Constitution the system was expanded into a system involving three branches with many checks and balances to try and keep any one branch of the system from becoming too powerful.
The Three Branches
The Executive Branch is made up of the President of the United States and the members of his cabinet and other officers. The power of the Executive is to enforce the laws passed by the Legislative Branch. One key power granted to the President is the Veto Power. This allows the President to not allow a passed law to be put into effect. The President also has the power to appoint members of the Judiciary or other Federal Offices when a vacancy is found there.
The second Branch is the Legislative Branch made up of the House of Representatives and the Senate. This branch has the power to pass laws and almost all of the business of actually running the country originates from here. If a law is vetoed they can overturn it if 2/3 of both houses vote to overturn the veto. They are also responsible for approving an appointment by the President to Federal Offices before they go into effect. They also have the power to Impeach a Member of the government if a crime is deemed to have been committed and can remove them from office.
The last branch is the Judicial made up of the Supreme Court of the United States and other lesser courts. It is the duty of the Supreme Court to decide whether a law passed by the Legislative Branch is valid. If they deem it in conflict with the US Constitution then they can declare if Unconstitutional. The Cheif Justice presides over any impeachment proceeding.
Republics in Fiction
In function most fictional republics are either based on the US Constitutional System or the Roman Senatorial System. The best fictional example of the later is the Galactic Republic of Star Wars. Even this does contain some portions of the multi-branch system of the US as a Central Court is mentioned. The United Federation of Planets appears to be a Republic-like system but how the Federation Council functions or is appointed is never adequately explained to really be sure.