Qualifiers are those things in parenthesis you see at the end of some tags. They serve to make the exact meaning of the tag clear so there is no confusion with other tags.
There are many types of qualifiers.
Many artists go by a short name that can be shared by other artists or characters. So Danbooru qualifies them with another text string that is related to that artist. It may be:
- the artist's website or blog name
- circle name
- The username (often different from their actual displayed name) that artist uses on a site like Pixiv, Twitter, DeviantART, Tinami, etc.
See howto:artist for more info.
For names of characters that can be confused with characters from other series, or with artists. If the series name is long, an abbreviation may be used for the qualifier.