Holidays

Unofficial holidays are not traditionally marked on calendars. These holidays are celebrated by various groups and individuals. Some promote a cause, others recognize historical events not officially recognized, and others are "funny" holidays celebrated with humorous intent. ... For example, Monkey Day is celebrated on December 14, International Talk Like a Pirate Day is observed on September 19, and Blasphemy Day is held on September 30. April Fool's Day on April 1 is also another example. — en.wikipedia.org