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.
... Inteligencia[?] (CNI[?]) (2002 - ) Sweden Säkerhetspolisen[?] (SÄPO) Switzerland Nachrichtendienst[?] (ND) Turkey Milli Istihbarat Teskilan[?] (MIT) Jandarma ...