A referendum is a direct vote in which the people are asked to either accept or reject a particular proposal, such as the adoption of a new constitution, a law, or a specific governmental policy. It is a tool for the expression of direct democracy. Referendums can be binding or advisory, and in some countries, different names are used for these two types of referendums. The term "referendum" covers a variety of different meanings, and the terminology is different depending on the country that holds them. Referendums can be further classified by who initiates them.

From a political-philosophical perspective, referendums are an expression of direct democracy, but today, most referendums need to be understood within the context of representative democracy. Referendums are used to express the wishes of the electorate with regard to government policy or proposed legislation. They exist in a variety of forms, and the referendum may be obligatory or optional. Under the obligatory type, a statute or constitution requires that certain classes of legislative action be referred to a popular vote for approval or rejection. Under the optional (or facultative) referendum, a popular vote on a law passed by the legislature is required whenever petitioned by a specified number of voters.

In conclusion, a referendum is a direct vote in which the people are asked to either accept or reject a particular proposal, and it is a tool for the expression of direct democracy. Referendums can be binding or advisory, and they exist in a variety of forms.