The Wraith, known as the Image in the international 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 many similar ghostly foes, the Wraith's touch causes Paralysis. Wraiths have the same vulnerabilities and resistances as most undead enemies have, and thus a quick Fire or Dia spell is the best tactic, and Fira can easily destroy an army of Wraiths.
Wraith is a Scottish dialectal word for "ghost," and/or "spirit".