Vanilla
From Destiny 2 Wiki
Something is classified as Vanilla if it was in Destiny 2 at launch or if it was added after launch but before the release of Curse of Osiris. For items, this can be easily identified by the lack of any special symbols in the upper-left corner of the item icon.
Accessibility
All Vanilla things are available to owners of the base game, even if they have been altered by the Curse of Osiris release or later game updates.
Holidays and Vanilla
As holiday-related Live Events were only introduced after the Curse of Osiris release, all things relating them are not classified as Vanilla even if they are available to owners of the base game.