Sede vacante is an expression, used in the Canon Law of the Catholic Church and the Church of England, that refers to the vacancy of the episcopal see of a particular church. It is Latin for "the seat being vacant" (the ablative absolute to sedes vacans "vacant seat"), the seat in question being the cathedra of the particular church.
Read more about Sede Vacante: Vacancy of The Holy See, List of sede Vacante Periods in The Holy See Since The 19th Century, For Roman Catholic Dioceses Other Than The Diocese of Rome, Other Uses