Black Triangle Meaning

(ufology) One of a class of triangle-shaped unidentified flying objects, usually with a light in each corner.

Example: Used other than as an idiom: see black,‎ triangle.
2005, Bill Foster, Peggy Foster, Nadine Wheeler, The Black Triangle Abduction, The Invisible College Press, page 22:
  Somewhere behind that blinking yellow light that black triangle was hovering, (or moving only a few miles per hour), in our direction, straight at us.
2007, Craig R. Lang, The Cosmic Bridge, Close Encounters and Human Destiny,, page 4:
  Note: The black triangle is a commonly seen UFO.
2009, Nick Redfern, Memoirs of a Monster Hunter,, page 105:
  On Thursday, July 15, 2004, I flew to Denver, Colorado, where I was scheduled to speak at the annual symposium of the Mutual UFO Network on the subject of a particular type of UFO that has become known as the “Black Triangle,” and one that has been seen regularly in the skies of practically every corner of the planet for approximately the last two decades.
2011, William J. Birnes, The Everything UFO Book: An Investigation of Sightings, Cover-ups, and the Quest for Extraterrestrial Life, Adams Media, page 229:
  Just three years after the Belgian black triangle incident, a similar craft appeared over RAF Cosford and RAF Shawbury.