Cursed Shard

A character at 110 with a Legion legendary can get the Cursed Shard a number of different ways, such as the Grand Challenger's Bounty cache, completing a random dungeon through the Dungeon Finder, Emissary Quest caches, and raid bosses.

As a quest objective
This item starts The Cursed Shard.

Speculation
The Cursed Shard might be an early form of Azerite.