The term is not an official one, but more of a description of the purpose of these individuals, on their transformation as a Vampire and eventual fate.
These are Vampires created by Xi Tai and the Followers of Set to act as blood gatherers to aid in his awakening using "The Evil Chain". They are often low-leveled Vampires because of this. Furthermore, they are not given the option to become anything but a blood crazed demon. Picking off humans, they gather strength and then are handed to him.
These Vampires are then either controlled by him or drained by him. Sometimes they lay low like sleepers, becoming active only when they need to be. This allows them to act as normal human beings during the day, hiding their true natures revealed at night, while they assess and pick off opportunities to find victims.
Never the less, the fact the Hunters' knew they existed meant they were not a secret and their existence was well observed by the group long before Xi Tai awakened.
Jalousie becomes one in the end. It is never stated whether or not it was intentional for her to become one, though it is presumably done on purpose as she was left to guard him.
Their purpose fits in with his own belief that consumption of the weak is what defines the strong.
|Followers of Set|
|misc. characters||Zhen Mi ● Jalousie ● Isis ● High Priest|
|Sacred Weapons||Rotting Bracelet|
|Misc.||Xue Yan ● Sacrificial Lamb|