Two Dee Ecks means: Konami’s famous arcade rhythm game beatmaniaIIDX. BeatmaniaIIDX had 20 versions of the game, starting with the first style and ending up with the 10th. Then we added IIDX Gold, Happy Sky. DistorteD. Gold. DJ Troopers. Empress. Sirius. Resort Anthem. Lincle. And the latest, Tricoro. There are many cabinets to be found in arcades, and you can also find HDD rips on the Internet. (in Community Dictionary, added by Aitor Martínez)