It is a neutral expression for a donor or victim, who is the person where the vampire gets the blood or energy. The craving to drink. Sometimes it's described as an addictional withdrawing feeling but is less painful. Manifests itself in ravenous attacks. There are more theories on how to do this than I could quote here.
Some theories insist that there is no possiblity of turning a human.
This is only possible with latent vampires. A term anyone uses in accordance to his own definitons. Since there is so much dispute over the correct definiton this term is avoided by many real vampires. They only use the characteristics of the vampire to make themselves more comfortable with their own identity. This very often overlaps with the gothic scene.