What was the name of the 1605 conspiracy commemorated by Bonfire Night?

The 1605 conspiracy commemorated by Bonfire Night was the Gunpowder Plot.

The plot was a failed attempt by a group of English Catholics to kill King James I and members of Parliament. Their plan was to blow up the House of Lords during the State Opening of Parliament on 5 November 1605. The conspirators hoped that a Catholic uprising would follow the destruction of the government.

Robert Catesby organized the conspiracy, while Guy Fawkes was assigned to ignite the explosives. The plan collapsed when an anonymous letter warned William Parker, 4th Baron Monteagle, to avoid Parliament. A search of the cellars found Fawkes and the gunpowder before the ceremony began.

The name is sometimes shortened to the Gunpowder Treason. It should not be confused with the Popish Plot of 1678, a fabricated conspiracy claim made more than 70 years later.