Considering helping out on the wiki to keep it updated - in particular the changed unique items need to be updated to reflect 2.6.0 changes.
Mods and base items have been updated to 2.6 values - skill progressions on some skill gem pages may need updating or some bugs need to be fixed.
Tags are internally used by the game to describe certain properties/aspects of entities. Those are then usually used later to govern certain rules about those entities, such as which modifiers can spawn which items.
Most entities, like monsters, areas, mods and items come with their own list of tags. The tags are used to describe some properties of those entities, for example currency items are usually tagged with