The Vacancy of the Holy See
(Papal Interregnum)

The period between the death or resignation of a Pope and the election of his successor, is formally referred to as "The Vacancy of the Apostolic See."
It can also be called the Papal  Interregnum, from the Latin for between the reign (of one Pope and another). It is a period governed by papal law, which admits of no changes to Church governance, or to the spiritual or material patrimony of  St. Peter, save the election of his successor.