In 1978 Japan’s Ministry of Economy, Trade and Industry established the encoding that would later be known as JIS X 0208, which still serves as an important reference for all Japanese encodings. However, after the JIS standard was released people noticed something strange – several of the added characters had no obvious sources, and nobody could tell what they meant or how they should be pronounced. Nobody was sure where they came from. These are what came to be known as the ghost characters (幽霊文字).
Ohhh … I like this kind of mystery! Thx to @InfoSecSherpa for the heads up!
UPDATE: & thanks to @polm23 for the original write up!