Tag aliases are used to fix a "canonical" version of a tag's name. This feature is used in a few different scenarios:

* Variant spellings, especially for character names ([[kyuubey]] → [[kyubey]])
* Synonyms ([[flame]] → [[fire]])
* Abbreviations for long tag names ([[gits]] → [[ghost_in_the_shell]])
* Silly in-jokes ([[alcohol]] → [[humanity's_friend]]; all of the tags listed on [[tag_group:waifus]])

When the antecedent tag (before the arrow) is added to an image, Danbooru automatically removes it and adds the consequent tag (after the arrow) in its place. The antecedent is otherwise treated as being identical to the consequent for searches and some other actions.

Tag aliases differ from [[help:tag_implications|implications]], where both tags remain on the image. In other words, aliases are for tags referring to the same thing, while implications are for situations where one tag describes a subset of the images belonging to another tag.

You can request that an alias be created by using the "tag alias request form":/booru/tag_alias_request/new.