"Game Over" is a line frequently used in the Saw series. In general, the line is used at the end of the films when the principal subject ultimately fails his or her game and is left to die. In Saw, "Game Over" is used when John awakes in the bathroom and seals Adam inside to rot.
Saw V is the only film in which there is no "Game Over'" line.
In Saw 3D, Hoffman says it to Jill when killing her with the original Reverse Beartrap as an act of revenge. The final "Game Over" line in the series is used by Lawrence Gordon, when he seals Hoffman in the bathroom, along with the decayed remains of Adam, Zep, Xavier, and Lawrence's severed foot, to die.