For the purpose of Wikipedia maintenance and administration, tags are brief messages that MediaWiki automatically places next to certain edits (or logged actions). (Depending on the context, edits are sometimes called changes to a particular article or the contributions of a particular editor.) Edit tags are visible on histories, recent changes and certain special pages.
Edit tags can be used to detect potentially harmful edits or software bugs. Tags also are used to identify how someone made an edit, such as via mobile, VisualEditor, or GettingStarted. Edit filter managers, that is, users given access to the edit filters, can direct an edit filter to tag those edits that match the filter. Additionally, tags can mark edits which have been subsequently reverted. Without needing special access level rights, you can filter the lists of edits on the User contributions or Recent changes special pages by entering a tag in the Tag filter field. The list of established tags is at Special:Tags, and includes an interface for administrators to manage tags.