The period between the death or resignation of a Pope and the election of his successor, when the See of Peter is vacant, is called the Interregnum. This Latin term means 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.
How a Pope is Elected
Voting Procedure
There are three phases to the election process. They are:
1) Pre-Scrutiny, during which ballots are prepared and distributed.
2) Scrutiny, during which the ballots are collected and counted.
3) Post-Scrutiny, during which the ballots are counted, checked and burned.
1. Pre-Scrutiny
During the Pre-Scrutiny the ballots are prepared and distributed, and, 9 Electors are chosen by lot to serve as 3 Scrutineers, 3 Infirmarii and 3 Revisers.
The Scrutineers are three Cardinal Electors chosen by lot to gather and count the ballots. They stand at the altar as the Electors come up individually to deposit their votes. One of them also collects the votes of those present who are not physically able to come up to the altar. Afterwards, sitting at a table in front of the altar they tabulate the ballots to determine if an election has occurred.
The Infirmarii are three Cardinal Electors chosen by lot to take ballots to Electors who although within the enclosure of the Conclave are too sick to be present in the Sistine Chapel. They take with them a locked box which, having been shown to the other Electors to be empty, receives the votes of the infirm. They return it unopened to the Scrutineers.
The Revisers are 3 Cardinal Electors chosen by lot to check the ballot count and the notes of the Scrutineers to determine if the tabulation of the ballots was carried out exactly and faithfully.
2. Scrutiny
After all ballots are in, including those brought from the sick by the Infirmarii, the 1st Scrutineer shakes the receptacle several times to mix the ballots. Then the 3rd Scrutineer counts them, placing them in a second, empty, receptacle. If the number of ballots does not equal the number of electors, they are burned, and a second vote taken immediately. Otherwise, the Scrutineers proceed to tabulate the vote.
Sitting at a table in front of the altar, the 1st Scrutineer silently reads the name on a ballot, passes it to the 2nd Scrutineer who does likewise, and then passes it to the 3rd Scrutineer, who reads the name aloud and then writes it down. Each Elector also writes it down on a sheet provided for this purpose. The ballot is then pierced with a needle through the word eligo (I elect) and placed on a thread for security.
When all ballots have been read the ends of the thread are tied in a knot and the ballots are placed in a receptacle on one end of the table.
3. Post-Scrutiny
The Scrutineers tabulate the vote count they recorded by individuals receiving votes. They do this on a separate sheet of paper from that on which the vote count was first made. The Revisers then verify the results.