The Wraith, known as the Image in the localized release of the NES version, is an enemy in the original Final Fantasy. Wraith is also the name used in the original NES translation to refer to the Specter.
Like similar ghostly foes, the Wraith's touch causes Paralysis. It has the same vulnerabilities and resistances as most undead enemies, and thus a quick Fire or Dia spell defeats them, and Fira can destroy an army of them.
Wraith is a Scottish dialectal word for "ghost," and/or "spirit".