KEY DISC

Key disc is a term referring to a game that, in the sense of Bemani games, does not need the capabilities of another game to be played. Pop'n Music 1, 2, 5, and 6, as well as all the PS2 games, are key discs, as is every beatmania IIDX, the first beatmania game (as well as Sound of Tokyo, Best Hits, and 6th Mix & Core), every Guitar Freaks game except the 2nd PlayStation one, all the Dance Dance Revolution games except the Club Append games, both Keyboardmania games, and ParaParaParadise.

A key discs can also be used to play an append disc, which can't be otherwise without another game first inserted into the PlayStation (or Dreamcast, if you're playing the DDR Club game or Pop'n Music 3 and 4).