Cool word, via Wikipedia:
An interregnum (plural interregna or interregnums) is a period of discontinuity of 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” + rēgnum, “reign” [from rex, rēgis, “king”]), and the concepts of interregnum and regency therefore overlap. An interregnum can simplistically be thought of as a “gap”, although the idea of an interregnum emphasizes the relationship to what comes before and to what comes after in a sequence. This contrasts with a near synonym like gap, which may be random, encompassing neither connotation of interjacency in a sequence nor formal interrelation.