Each piece has a slot (the groove) cut all along one edge, and small outcrop (the tongue) on the opposite edge. Two or more pieces thus fit together.
... (+ 1977) February 5 - Walter Gross[?], cabaretist (+ 1989) February 7 - Ernst Ginsberg[?], actor and film director (+ 1964) February 11 - Henry LaBouisse[?], ...