This is one of the tags that can be added to Wiki articles to denote how closely it adheres to official sources published by Wizards of the Coast.

"Unofficial Material" covers topics that would break or at least radically change the setting - the inclusion of spelljammer ships, using the Great Wheel cosmology with Eberron, new Dragonmarked Houses and similar powerful organizations, and so on.

For more details, see the Eberron Wiki FAQ.