Ghost

From Guild Wars Wiki

Ghosts are the souls of formerly living creatures. They are easily recognized by their translucent appearance and their usually greenish skins.

There are exceptions, but most of them are non-fleshy, leave invisible non-exploitable corpses and take double damage from Holy damage sources.
Almost every single NPC with a translucent and greenish appearance is a ghost, although not many of them are hostile to the players. Examples of allied ghosts are the Ghostly Hero, the Tormented Souls or the Eternals.

Although spirits have also translucent and greenish skins, they are different families and should not be confused with ghosts.

[edit] List of hostile NPCs

Region	Army	Name	Trophy
Core
The Underworld	Underworld army (hostile)	24 (26) Smite Crawler 28 (30) Banished Dream Rider 27 (30) Mindblade Spectre 28 (30) Wailing Lord	Phantom Residue
Prophecies
Ascalon	Unkown	10 (24) Spirit of the Fallen1	Ghostly Remains
Kryta	Undead army	11 (24), 17 (25) Wraith 17 (25) Smoke Phantom	Decayed Orr Emblem
Crystal Desert	Underworld army (hostile)	28 (30) Banished Dream Rider	Phantom Residue
Ring of Fire Islands	Undead army	24 (26) Portal Wraith	Decayed Orr Emblem
Nightfall
Istan	Undead army	15 (25) Tomb Wraith	Skeleton Bone
Realm of Torment	Undead army	24 (26) Portal Wraith	Decayed Orr Emblem
Domain of Anguish	Domain of Anguish army	28 (30) Greater Dream Rider	Titan Gemstone
Eye of the North
Depths of Tyria	Undead army	15 (25) Restless Spirit 20, 21, 22, 23, 24 (26) Crypt Banshee 24 (26) Restless Spirit 20, 21, 22, 23, 24 (26) Crypt Wraith 24 (26) Servant of Murakai 20, 21, 22, 23, 24 (26) Shock Phantom 20, 21, 22, 23, 24 (26) Ash Phantom 24 (?) Damned Crewman	Undead Bone
	Slavers' Exile army	28 (30) Restless Dead 28 (30) Restless Dead	Undead Bone
Far Shiverpeaks	Undead army	20, 21, 22, 23, 24 (26) Shock Phantom	Undead Bone

1. These ghosts are vulnerable to holy damage
2. These ghosts are fleshy creatures