A puzzle whose solution relies on external sources such as tables, dictionaries, Wikipedia, or specifics that may not be common knowledge.
The knowledge tag should be used for puzzles that require specific knowledge about the subject matter to be able to answer, or require external help (i.e. tables, dictionaries, Wikipedia, Google, etc.).
Note there are also tags for more specific knowledge sets such as:
* music
* video-games
* movies
* history
