What is "purple triangle"

n. 1 (context derogatory dated English) a Jehovah's Witness 2 (context historical English) a Jehovah's Witness in Nazi Germany

The purple triangle was a concentration camp badge used by the Nazis to identify Bibelforscher (the German name for the Bible Student movement) in Nazi Germany. The classification applied primarily to Jehovah's Witnesses, but included members of other Bible Student splinter groups, as well as Adventists, Baptists, and pacifists. Nazism opposed unorthodox-Christian religious minorities (along with Jews), but made the Bible Students the object of particularly intense persecution, including such extensive incarceration that a distinct badge was assigned to them.