From the ancient practice of announcing the result of a papal election. If the election was successful, i.e. a candidate received two-thirds majority in the College of Cardinals, the inspected ballots were burned in the stove of the Sistine Chapel of Vatican, resulting in white smoke spewing out from the chimney. If the required majority was not reached, damp straw was added to the stove, resulting in black smoke.
- The announcement to the outside world that a conclave has chosen a new Pope.
- (figuratively) An event of reaching an agreement.
- Sit yourselves down together until the white smoke comes out.