Answer:
What is a referendum?: A referendum (plural: referendums or less commonly referenda) is a direct vote by the electorate on a particular proposal or issue. This is in contrast to an issue being voted on by a representative. It can have nationwide or local forms. This may result in the adoption of a new policy or specific law. In some countries, it is synonymous with or commonly known by other names including a plebiscite, votation, popular consultation, ballot question, ballot measure, or proposition.
When did it take place in the UK for Brexit?: 23 June 2016