A femme fatale literally means "fatal woman" in French.
According to the infamous Wikipedia, "a femme fatale is a mysterious and seductive woman whose charms ensnare her lovers in bonds of irresistible desire, often leading them into compromising, dangerous and deadly situations. She is an archetype of literature and art." A femme fatale knows what she wants and goes for it. Are you a femme fatale?
I think the most famous femme fatale of them all is Cleopatra. Technically her name is Cleopatra VII Philopator and she is known as the last pharaoh of Ancient Egypt. She married her brother (yuck) but eventually become sole ruler and had relationships with Julius Caesar and Mark Antony. Unfortunately she committed suicide after her incredible rise to power but her story lives on today.