Source: http://en.wikipedia.org/wiki/Referendum
A referendum (in some countries synonymous with plebiscite — or a vote on a ballot question) is a direct vote in which an entire electorate is asked to vote on a particular proposal. This may result in the adoption of a new constitution, a constitutional amendment, or a law.
Referendum is the gerund of the Latin verb refero, and has the meaning "bringing back" (i.e. bringing the question back to the people). The term plebiscite has a generally similar meaning in modern usage, and comes from the Latin plebiscita, which originally meant a decree of the Concilium Plebis (Plebeian Council), the popular assembly of the Roman Republic.
Today, a "referendum" can also often be referred to as a "plebiscite",
but in some countries they refer to different types of votes, differing
in their legal consequences.
Referendums and referenda are both commonly used as plurals of referendum. However, the use of referenda is deprecated by the Oxford English Dictionary, which advises that:
Referendums is logically preferable as a plural form meaning ballots on one issue (as a Latin gerund, referendum has no plural). The Latin plural gerundive referenda, meaning things to be referred, necessarily connotes a plurality of issues.
In the United States, a referendum is also typically known as an initiative when originating in a petition of ordinary citizens, and as a
referendum only if it consists of a proposal referred to voters by the
legislature. A referendum can be considered a kind of election and is often referred to as such in the U.S. (an election literally means a choice). In other countries, the term election is often reserved for events in which elected representatives are chosen.
From a political philosophical perspective, referendums are an expression of direct democracy.
However, in the modern world, most referendums need to be understood as
an element of systems that are predominantly representative in
character. As such, they tend to be used quite selectively, covering
issues such as changes in voting systems, where currently elected
officials may not have the legitimacy or inclination to implement such
changes.
Most of the time, when the citizens of a country are invited to vote, it is for an election.
However, people can also vote in referendums. Since the end of the
eighteenth century, more than five hundred national referendums were
organised in the world; among them, more than three hundred were held in
Switzerland.[1] Australia ranked second with dozens of referendums.
A referendum usually offers the electorate only two choices, either
to accept or reject a proposal, but this may not necessarily be the
case. In Switzerland, for example, multiple choice referendums are common; two multiple choice referendums held in Sweden, in 1957 and 1980, offered voters a choice of three options; in 1977 a referendum held in Australia to determine a new national anthem was held in which voters were presented with four choices; and in 1992,
New Zealand held a five-option referendum on their electoral system.
A multiple choice referendum poses the question of how the result is
to be determined if no single option receives the support of an absolute
majority (more than half) of voters - a proviso for some; others regard a non-majoritarian methodology like the Borda count as more inclusive and more accurate. This question can be resolved by applying voting systems designed for single winner elections to a multiple-choice referendum.
Swiss referendums get around this problem by offering a separate vote
on each of the multiple options as well as an additional decision about
which of the multiple options should be preferred. In the Swedish case,
in both referendums the 'winning' option was chosen by the Single Member Plurality ("first past the post") system. In other words the winning option was deemed to be that supported by a plurality,
rather than an absolute majority, of voters. In the 1977 Australian
referendum the winner was chosen by the system of preferential instant-runoff voting.
The 1992 New Zealand poll was counted under the two-round system, as
were polls in Newfoundland (1949) and Guam (1982), for example.
Although California does not have deliberate multiple-choice referendums in the Swiss or
Swedish sense (in which only one of several counter-propositions can be
victorious, and the losing proposals are wholly null and void), it does
have so many yes-or-no referendums at each Election Day that the State's
Constitution provides a method for resolving inadvertent conflicts when
two or more inconsistent propositions are passed on the same day. This
is a de facto form of Approval Voting - i.e., the proposition with the most "yes" votes prevails over the others to the extent of any conflict.
Other voting systems which could be used in multi-option referendums are the Borda and Condorcet rules.