The Specter, also known as the Wraith in the Nintendo Entertainment System version, is an enemy in the original Final Fantasy. In the Game Boy Advance Dawn of Souls remake, the Specter and the Wraith are two different enemies.
They only appear as common random encounters in Basement Floors 1 and 2 of the Cavern of Ice. When the party falls down through a hole in B2F, they land in a small room, where they must fight groups of Specters, Wraiths, and Ghasts to escape.
As with all undead enemies, Specters are weak to Fire and Dia attacks. Like the other ghost-type enemies, its physical attacks may cause Paralysis. Strong physical attacks will work as well, due to their low HP.
Wraith is a Scottish dialectal word for "ghost," and/or "spirit".