From Wikipedia (H/T Rick Garnett on PrawfsBlawg for the Reminder):
Guy Fawkes Night is an annual celebration on the evening of 5 November. It marks the downfall of the Gunpowder Plot of 5 November 1605, in which a number of Catholic conspirators, including Guy Fawkes, attempted to blow up the Houses of Parliament, in London, United Kingdom.
Every see V for Vendetta? You know the story. Some other coverage here and here.
Please don’t report me to flag @ whitehouse.gov for celebrating this holiday. Kthxbye.