Tags without categories and/or descriptions are considered “unsorted” and should generally be avoided when manually adding tags to scenes.
If a tag doesn’t have a category or description, then it is likely still unsorted. It will usually have a sparse or non-existent edit history as well. This means it’s exact usage hasn’t been determined yet, no potential merge targets have been found, and no decision has been made on if it’s even worth keeping. It’s usually preferable to avoid unsorted tags when manually adding them to a scene yourself. If you’re just adding scraped tags though, don’t worry if they’re currently sorted or unsorted. More scraped sources for an unsorted tag could help us decide what to do with it in the future. Finally, if you want to find a quick list of sorted tags, lean on the Tag Categories page of StashDB. Every tag with a category assigned will be organized to some extent already.