Help:Tags

A tag (also referred to as a change tag) is....

Automatically applied tags
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Adding or removing tags from a revision or log entry
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Tag management
Users with the  user right (administrators by default) can use the Special:Tags special page to create, delete, activate and deactivate tags.

Creating a tag
You may create a new tag which will be applied manually by users. The name of the tag must satisfy the following criteria: To do this, use the form at the top of Special:Tags. (If you do not see the form, you do not have permission to create tags.) The reason you provide will be entered into the tag management log.
 * it must not contain the comma or forward slash  characters;
 * it must not contain characters that are prohibited in page titles (for example, ); and
 * it must not be reserved by an extension.