A voting system or electoral system consists of the set of rules which must be followed for a vote to be considered valid, and which set out how votes are cast, counted and aggregated to yield a final result of an election or a referendum. Common voting systems are majority rule, proportional representation and plurality voting, with a number of variations and methods such as first-past-the-post and preferential voting. The study of formally defined voting systems is called social choice theory or voting theory, a subfield of political science, economics, or mathematics.

Those who are unfamiliar with voting theory are often surprised to learn that voting systems other than majority rule exist, or that disagreements exist over what it means to be supported by a majority. Depending on the meaning chosen, the common “majority rule” systems can produce results that the majority does not support. If every election had only two choices, the winner would be determined using majority rule alone. However, when there are more than two options, there may not be a single option that is most liked or most disliked by a majority. A simple choice does not allow voters to express the ordering or the intensity of their feeling. Different voting systems may give very different results, particularly in cases where there is no clear majority preference.


Source: Wikipedia