The story
Partial calque of German Lenné-Dreieck: Dreieck → triangle.
Etymology from Wiktionary, CC BY-SA 4.0.
Lenné Triangle
Today it means: The gore delineated by the Bellevue-, Ebert-, and Lennéstraßen which, between 1961 and 1988, was part of the German Democratic Republic de jure, but was separated from it by the Berlin Wall, which ran along the Ebertstraße. Full definition →