There are a bunch of different tags that can be used. You have the primary tags, which are your main tags that you must have 1 of and only 1. You then have Secondary tags, in which can be used on any discussion, or you can tie it to a primary. These secondary tags you can have up to 3.
You may request new tags here if you do not see a tag that relates to a topic and I or one of our mods can see about adding it to the forum. Make sure to start a new discussion.