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).
This article is underwhelming. Despite being in English, it links to a Japanese Wikipedia article. The English Wikipedia article has all the same info as this post and more: https://en.wikipedia.org/wiki/Ghost_characters
tl;dr: some Japanese kanji from older encodings were carried forward into new ones. But some of those characters were difficult or impossible to identify. Most were archaic place names or transcription errors.
This article is underwhelming. Despite being in English, it links to a Japanese Wikipedia article. The English Wikipedia article has all the same info as this post and more: https://en.wikipedia.org/wiki/Ghost_characters
tl;dr: some Japanese kanji from older encodings were carried forward into new ones. But some of those characters were difficult or impossible to identify. Most were archaic place names or transcription errors.
I like the article. Interesting subject, well written and it has the perfect lenght.