User blog comment:Fintin/What is One Piece?/@comment-66791-20101102140906

I'm calling it: One Piece is a weapon. More specifically, One Piece is one of the ancient weapons, like Plutons, that can only be discovered through the Poneglyphs. I'm guessing this because Shiki said Roger discovered a powerful weapon right before the Edd War. Then Whitebeard said when One Piece was discovered, the world will erupt into a great war, or something like that.

These clues lead me to believe that One Piece is probably a very powerful weapon, something which a lot of people will fight over and only someone like Roger (or Luffy) should be in control of.