vacancy

In politics, a casual vacancy (casual in the sense of "by chance") is a situation in which a seat in a deliberative assembly becomes vacant during that assembly's term. Casual vacancies may arise through the death, resignation or disqualification of the sitting member, or for other reasons.
Casual vacancies have the effect of eliminating or reducing the representation for the member's constituency. Accordingly, many jurisdictions provide by law for the speedy filling of vacant seats.
Casual vacancies can also occur in non-governmental assemblies, such as boards of directors and committees of voluntary organisations.
Methods of filling a casual vacancy to an elected body include:

by-election or special election, of the same electorate which voted in the vacating member
co-option, by the remaining members of the body
appointment or nomination, by a different body or office holder
automatic succession, of a substitute or from a replacement list, fixed at the time of the original election
countback, used in single transferable vote elections: recounting the ballots of the original election and redistributing those allocated to the vacating member

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