Vampires are a race of predators who feed on blood. They were once humans transformed by a conscious act of will, known as the Embrace, into powerful creatures of the night. During the Embrace, a vampire drains a candidate of all their blood and replaces it with a small amount (generally a single drop) of their own. This causes the corpse to rise as a new vampire, usually instantly. The vampire who initiates the Embrace is the Sire; the new vampire is the Sire's Childe.
*via the White Wolf wiki*