Simply put, a conclave is the assembly of cardinals that elects a pope. The word itself comes from the Latin "com" and "clavis," meaning "together" and "key," respectively – highlighting the absolute, behind-closed-doors secrecy with which the cardinals conduct their discussions and balloting.

Before the closed-door conclave to elect Pope Francis' successor, Catholic cardinals have gathered in the Vatican for a final Mass and exhortation.

The papal conclave begins May 7. Here's how cardinals choose the next pope, what to expect and how secretive the process is.