The restless dead (colloquially known as the undead) is a collection of creatures who have lost their spirits (the tether between their soul and their body), most commonly by death.
Undead: A reanimated corpse that may or may not still retain its original soul
Zombie: An undead with an aggressive nature but lacks advanced motor skills required to seek out prey
Ghoul: An undead with an aggressive nature that actively seeks out creatures to kill and sometimes consume
Draugr: An undead with a defensive nature that will often lie dormant until its designated area is disturbed
Lich: An undead with full mental capability, but with a rotting (or sometimes skeletal) body
Revenant: An undead with full mental and physical capability
Spirit: A soul that has lost its original body and may or may not possess another
Phantom: A passive spirit that often remains undetected
Specter: A passive spirit that is visible to most
Poltergeist: A spirit that has possessed another body and/or object – may or may not be hostile
Wraith: A highly hostile spirit that often seeks vengeance for an untimely or especially horrific death – may or may not have poltergeist-like abilities
Shade: A highly hostile and artificial spirit that was once a specter or phantom – it has been altered through necromancy into a weaponized version of a wraith
Other: Unique cases where the body and soul still exist in the mortal realm but they have been separated for some reason
Lemure: A hostile spirit, often one that died in battle and who’s body wasn’t properly taken care of, that wanders forever until it reunites with its body or the body is destroyed – the body also usually wanders until it finds the soul
Exploited: When the spirit is inhibited through magical means, allowing the caster to seize control of the body while the soul still resides there