Specify a list of tags to keep hidden: These tags will be invisible to users,
such as in tag clouds or in post tags lists. This is useful when using tags to
control behavior of your blog, or when you wish to maintain groupings of posts
out of the public eye.
This does not prevent tag archives for hidden tags from being accessible, only
hides tag links from tag lists and tag clouds.
Capable users (with the see_hidden_tags capability,) can see hidden tags in
tag lists (but NOT tag clouds.) Hidden tags will receive the .hidden-tag class
and are grayed out by default.