Dungeons and Dragons is a Pen and Paper Role play game.
The numbers indicate the edition of that RPG I am referring to.
Each edition got its own writing of the Name of the game.
3.5 was the Edition that was the actual one, when the DVD limited edition was released, while the 1st edition should be the one, when the show was aired, if I am correct.
The 2nd Edition of the game got another name “Advanced Dungeons & Dragons”