Succubus

In folklore traced back to medieval legend, a succubus is a female demon or supernatural entity that appears in dreams, who takes the form of a human woman in order to seduce men, usually through sexual intercourse. The male counterpart is the incubus. Religious traditions hold that repeated intercourse with a succubus may result in the deterioration of health or even death.

In modern fictional representations, a succubus may or may not appear in dreams and is often depicted as a highly attractive seductress orenchantress; whereas, in the past, succubi were generally depicted as frightening and demonic.

Source: http://en.wikipedia.org/wiki/Sucubus