A voting system (or electoral system) is a set of rules that determine how elections and referendums are conducted and how their results are determined. Some voting systems elect a single winner (single candidate or option), while others elect multiple winners, such as members of parliament or boards of directors. The study of formally defined electoral methods is called social choice theory or voting theory, and this study can take place within the field of political science, economics, or mathematics, and specifically within the subfields of game theory and mechanism design.