Usually refers to a ghost or another type of apparition. It may also refer to an optical illusion called a brocken spectre. According to William Blake, it is one aspect of the fourfold nature of the human psyche.
Specter appears in the Amala Network as a boss three times. Each time, he starts alone before calling in five more Specters. In the first battle, after a certain time, any Specters that are alive will merge into one stronger Specter. The number of fused Specters determines how strong the single Specter is. This battle is set before the Demi-Fiend can open a path to Ginza through the Amala Network.
Later on in the game, the Specter is once again fought in the network when the Demi-Fiend tries to check on how Isamu is doing, engaging him in a fight. The last time the Specter encounters the Demi-Fiend is when he goes after Jyoji Hijiri when Isamu whisks him away.
"A spirit of the dead in Western folklore. Its name means "fear." A specter's appearance is said to be horrifying beyond anything imaginable. Those to whom it appears are paralyzed with fear, but are very rarely harmed. Specters are often confused with phantoms, but whereas specters represent fear, phantoms represent illusion."
—Shin Megami Tensei IMAGINE Compendium
Specter can be contracted in Ueno at night, the Old Tokyo Metro, and Ichigaya Camp's silver-level instance. A nightmare variant can be encountered in Ichigaya Camp's gold-level instance with a 90% chance to null any magical attack.