Interregnum

An interregnum (plural interregna or interregnums) is a period of discontinuity or "gap" in a government, organization, or social order. Archetypally, it was the period of time between the reign of one monarch and the next (coming from Latin "inter-", "between" and "rēgnum", "reign" [from "rex, rēgis", "king"]), and the concepts of interregnum and regency therefore overlap. Historically, the longer and heavier interregna were typically accompanied by widespread unrest, civil and succession wars between warlords, and power vacuums filled by foreign invasions or the emergence of a new power. A failed state is usually in interregnum.
The term also refers to the periods between the election of a new parliament and the establishment of a new government from that parliament in parliamentary democracies, usually ones that employ some form of proportional representation that allows small parties to elect significant numbers, requiring time for negotiations to form a government. In the UK, Canada and other "first past the post" electoral systems, this period is usually very brief, except in the rare occurrence of a hung parliament as occurred both in the UK in 2017 and in Australia in 2010. In parliamentary interregnums, the previous government usually stands as a caretaker government until the new government is established.
Similarly, in some Christian denominations, "interregnum" (interim) describes the time between vacancy and appointment of priest or pastors to various roles. Additionally, the term has been applied to the period of time between the election of a new President of the United States and his or her inauguration, during which the outgoing president remains in power, but as a lame duck.
Historical periods of interregnum.
Particular historical periods known as interregna include:
In some monarchies, such as the United Kingdom, an "interregnum" is usually avoided due to a rule described as "The King is dead. Long live the King", i.e. the heir to the throne becomes a new monarch immediately on his predecessor's death or abdication. This famous phrase signifies the continuity of sovereignty, attached to a personal form of power named "Auctoritas". This is not so in other monarchies where the new monarch's reign begins only with coronation or some other formal or traditional event. In the Polish–Lithuanian Commonwealth for instance, kings were elected, which often led to relatively long interregna. During that time it was the Polish primate who served as an interrex (ruler between kings). In Belgium the heir only becomes king upon swearing before the parliament.
Christianity.
Catholicism.
A "Papal interregnum" occurs upon the death or resignation of the Catholic Church's Pope, though this is generally known as a "sede vacante" (literally "when the seat is vacant"). The interregnum ends immediately upon election of a new Pope by the College of Cardinals.
Anglicanism.
"Interregnum" is the term used in the Anglican Communion to describe the period before a new parish priest is appointed to fill a vacancy. During an interregnum, the administration of the parish is the responsibility of the churchwardens.
Mormonism.
In the Church of Jesus Christ of Latter-day Saints, when the President of The Church dies, the First Presidency is dissolved and the Quorum of the Twelve Apostles (the Twelve) becomes the Church's presiding body. Any members of the First Presidency who were formerly members of the Twelve rejoin that quorum. The period between the death of the President and the reorganization of the First Presidency is known as an "Apostolic Interregnum".
Chess.
FIDE, the world governing body of international chess competition, has had two Interregnum periods of having no chess champions, both during the 1940s.