The following referes to vampires as depicted in White Wolf's World of Darkness & Old World of Darkness role-playing games' universes.
In White Wolf Game Studio's role-playing games about vampires, vitae is a synonym of blood, especially as the symbol of life (cf Latin vita, "life"—whence English "vital"—and the derived phrase aqua vitae, or "water of life").
Vitae is the blood of living creatures from which vampires feed, and also the blood that circulates within the undead vampiric body. This blood is indeed the only, absolutely necessary substance for the vampire, who gains no nourishment from food or drink (some vampires can tolerate ingesting other substances, but their bodies cannot process or dispose of them). Vitae is the vampire's single, eternal and constant obsession.
A vampire can only take a fixed amount of vitae within his body (the mechanics of Vampire: The Masquerade and Vampire: The Requiem measure this amount in "blood points", while Vampire: The Requiem uses vitae as a unit of measurement). Every night he loses a part of this reserve (one blood point), and feels the need for more.
If a vampire cannot consume vitae for some time, he will become more and more thirsty and may eventually enter a frenzy, during which he will lose control and attempt to get blood from whoever comes near, until the frenzy subsides. It is very possible that this does not happen immediately even after he is satiated. When a vampire loses all his vitae reserve, he will lose his ability to move or react, and his body will begin to deteriorate and he will enter a state of suspended animation knows as torpor, until blood is supplied again (a frenzy might ensue as soon as the body is able to move again).
Vitae may be gained from mortal human beings (called kine, as in cattle, by vampires), or from animals, or from other vampires. However, drinking another vampire's blood is potentially dangerous, since it may lead to complete dependency (a "blood bond"). Vampire vitae may be forced on mortal subjects to create ghouls or revenants, with effects similar to those of the blood bond. Older, more powerful vampires lose the ability to feed on animals, and, eventually, humans.
Uses of Vitae
Vitae is not only what keeps a vampire alive. Vitae can be used for Disciplines & types of Blood Magic. The supernatural abilities; (I.E. super speed) are produced by a Kindred/vampire focusing his/her vitae.
A Vampire's Vitae can be used to create a Ghoul or even to create a Blood Bond.
Blood Bond
If a Kine, Ghoul or Kindred drinks a vampire's blood 3 times they have entered into what is referred to as a 'Blood Bond'. Many Elder vampires will have a younger vampire under a partial Blood Bond --common with Tremere. The Tremere have their new members take part in a ritual known as the Transubstantiation of Seven. This binds the new Apprentice to the Council of Seven.
The only way to not risk becoming Blood Bound is to have the Merit of Unbondable (3-point Merit). The terms are often 'Thrall' for the one bound & Regnant for the one in control. A Vampire can be partially bound to as many vampires as they drink from, unless they are fully bound to one --then they become unbondable to anyone but their Regnant. All Childer are 1/3 Blood Bond to their Sires at the time of the Embrace.
First Drink: The drinker begins to experience intermittent but strong feelings about the vampire. She may dream of him, or find herself "coincidentally" frequenting places where he might show up. There is no mechanical effect at this stage, but it should be role-played. All childer have this level of bond toward their sires, for the Embrace itself forces one drink upon the childer; they may love their "parents," hate them, or both, but are rarely indifferent toward them.
Second Drink: The drinker's feelings grow strong enough to influence her behavior. Though she is by no means enslaved to the vampire, he is definitely an important figure in her life. She may act as she pleases, but might have to make a Willpower roll to take actions directly harmful to the vampire. The vampire's influence is such that he can persuade or command her with little effort (Social rolls against the thrall are at -1 difficulty).
Third Drink: Full-scale blood bond. At this level, the drinker is more or less completely bound to the vampire. He is the most important person in her life; lovers, relatives and even children become tertiary to her all-consuming passion. At this level, a regnant may use the Dominate Discipline on a thrall, even without the benefit of eye contact. Merely hearing the regent's voice is enough. Additionally, should the thrall try to resist the Dominate for some reason, the difficulty of such resistance is increased by two. Naturally, a higher-generation vampire still cannot use Dominate on a lower-generation thrall._____World of Darkness: New York FAQ
The way to break a Blood Bond is to avoid further consumption of the Regnant's blood (along with expending a great deal of Willpower), or to kill the Regnant (though this can cause side effect often described as "shattering [metaphorical] glass" and isn't guaranteeable). Forces such as true love may also negate a Blood Bond.