Its meaningless except in context. To me, the splatbooks, BoVD, etc. aren't any more official than say, the Quint books, or Bad Axe's race books. Official means at the minimum the PHB, DMG, and MM.
Then there are settings. For instance, FRCS, Monsters of Faerun, and Magic of Faerun would all be official to a standard Forgotten Realms campaign. But this doesn't have anything to do with the publisher. For a Scarred Lands game, Relics and Rituals and the Creature Collection would be official.
What it really comes down to is official is anything the DM says is part of his world.
The idea that "official == TSR" is an idea from the 80s, when there were companies producing compatible materials without license. Gary was making it clear that these materials wouldn't be acceptable at a tournament or convention games. They have nothing to do with 3e or the d20 license.
Then there are settings. For instance, FRCS, Monsters of Faerun, and Magic of Faerun would all be official to a standard Forgotten Realms campaign. But this doesn't have anything to do with the publisher. For a Scarred Lands game, Relics and Rituals and the Creature Collection would be official.
What it really comes down to is official is anything the DM says is part of his world.
The idea that "official == TSR" is an idea from the 80s, when there were companies producing compatible materials without license. Gary was making it clear that these materials wouldn't be acceptable at a tournament or convention games. They have nothing to do with 3e or the d20 license.