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 aren't mentioned in the books, but that would easily fit into the setting without "breaking it" - minor NPCs and organisations, new locations, descriptions of towns that are only mentioned on the maps or not at all, new minor spells, and so on.

For more details, see the Eberron Wiki FAQ.