vBulletin Manual - Tag Manager

Tags are a form of meta-data that enables structured searching on data that can’t easily be represented otherwise. You may define any tags you wish. Common tag uses include:

Topic or keyword
Actions required (for example, "requires review")

Upon entering the tag manager, you will see a list of tags:

To delete one or more tags, simply tick the appropriate checkboxes and click delete.

To add a tag, use the form at the bottom of the page:

Tags may contain any text you wish, though they should be less than 50 characters long. Depending on permission settings, tags may be created via the front-end dynamically.