These are private thread tags created by users then invited into them.
If you don't want them to show for you, you can click "My Private Thread Tags" at the top of the forums (next to simple filter, advanced filter, and classic mode), then you can choose to leave those thread tags, and you'll no longer be in them.
If you want them deleted from your forums altogether, you can head to Admin > Thread Tags, and you'll see a separate Private Thread Tags section at the bottom where you can administrative capabilities to delete them.
For more information, I recommend seeing the Private Thread Tag functionality listed in the
About our Forums article.