A ghost word is a word published in a dictionary or similarly authoritative reference work even though it had not previously had any meaning or been used intentionally. A ghost word generally originates from readers interpreting a typographical or linguistic error as a word they are not familiar with, and then publishing that word elsewhere under the misconception that it is an established part of the language.
Once authoritatively published, a ghost word occasionally may be copied widely and enter legitimate usage, or it may eventually be discovered and removed from dictionaries.