This is the sword used by Darkness (played by Tim Curry), in the final battle with Jack (Tom Cruise). Darkness is ultimately killed by his own sword, for Jack cuts his arm with it, sending him into the Abyss. [PiH]
The following are images from the DVD edition. The sword has an enormous amount of screen-time during the epic battle, being wielded by Tim Curry as Darkness and, in the end, by Tom Cruise, as Jack. This is not only the sword of Darkness, but also the sword that kills Darkness!