The undead exist in a kind of limbo between life and death. Not quite alive but not quite deceased, undead are often reviled, shunned, and feared - often for good reason. While some believe that the undead are bereft of a soul, others maintain that it is the soul's inability to depart the physical body that defines undeath.
The undead are fundamentally different from the living in many ways. They can be "killed," but their souls do not embark on the same journey as those of the living. Instead, their physical bodies seem to change, reforming at a later time.
Different varieties of undead have been observed. Among them are multiple sects of vampires, known as Consanguine. Vampires, unlike other undead, require blood of the living to sustain themselves. Why this is is not yet known, but it is clear that there are many differences even among the undead.
Many guilds categorically refuse to admit undead, and indeed the divine nature of some guilds' power may well be anathema to the walking dead. Others, though, welcome and even promote undead membership. The Teradrim, for example, require members to become undead before advancing to full membership status. And the Bloodborn are a guild composed entirely of Consanguine, their power seemingly passed through the transfer of blood between sire and progeny.
Once the curse of undeath has been accepted, it is permanent. However, rumors exist of a rare 'cure' available with the help of a certain divine power.