What is an "authorized" VST?

Soundwise

Noel Borthwick [Cakewalk]As you authorize them they will appear in SONAR.

Well, then how about if a plugin requires authorization within a DAW?

indeed, how else does one authorise? some plugins have a separate little app to do it, others a standalone version of the plugin, but the majority needs loading in a host to complete authorisation... and those "demo mode until authorised" plugs - much like sonar's new licensing/authorisation - where do they stand?

I think the wording of that might be confusing - it doesn't affect demos. The changes are only indirectly related to authorization. I'll try and explain.
Basically VST2 and VST3 dll's can contain multiple modules. e.g a single Waves DLL can contain hundreds of plugins.
The individual plugins in the dll will only work if they are authorized by the plugin vendor. In the case of Waves you do this via Waves License manager (WLM). Licences can be moved between ILok's or different computers so if you have a set of plugins authorized and move the license they now become unauthorized on that PC.
 
With the new changes SONAR will automatically rescan the dll and detect that it contains fewer plugins and remove all the old plugins from the VST cache so you won't see them anymore. That is all. Prior to this, under some conditions the old plugins could get left behind, leading to confusion. ie. they would appear in menus but if you tried to insert them they would fail. Also there were cases when you authorized a new set of plugins from the dll without updating the dll itself, SONAR wouldn't pick them up since it thought the package was up to date. This is why sometimes people had to force a rescan to see these plugins. Hope this helps explain it.