Glaive of the Aspects

The Glaive of the Aspects is a powerful weapon originally created by demons during the War of the Ancients. It was shattered into shards after the defeat of Archimonde and his champions at Mount Hyjal. After the reopening of the Dark Portal, Highlord Kruul, under Doom Lord Kazzak's command, set out in search of the shards. They were discovered and the glaive was reforged, however it current whereabouts are unknown.

Aspect Shards
The Aspect Shards are mysterious objects that Highlord Kruul, Field Commander of the Burning Legion's forces in Azeroth, is looking for. They were never seen in-game, except in the Highlord's yells.

Story
From Raid - Doom Lord Kazzak on the Official site:

When the Burning Legion began its second invasion of Azeroth, Lord Kazzak served as one of the unholy army's greatest generals. At that time the Legion possessed a powerful weapon called the Glaive of the Aspects. Forged by demons during the War of the Ancients, the glaive was imbued with the forces of earth, time, dream, magic, and life: powers taken from the mighty dragons. Even so, Archimonde and his champions were defeated during the Battle of Mount Hyjal, and the glaive was shattered. Knowing the Third War had been decided, Kazzak was forced to withdraw. In the war's aftermath, the shards of the glaive were hidden away for safekeeping. Recently Kazzak and his minions reactivated the Dark Portal, and Kazzak went through the portal to take command of the Legion's forces in Outland. In his absence, he entrusted his most powerful lieutenant, Highlord Kruul, with retrieving the Aspect Shards. In time Kruul succeeded, and the mighty glaive was reforged. With the Glaive of the Aspects and the raging desire to scour all life from the universe, the Legion may prove unstoppable.

Quotes

 * Highlord Kruul: "Your fate is sealed, Azeroth! I will find the Aspect Shards, and then you will not stand against our might!"