In your opinion, what exactly is a "witch"?

The definitions seems to be subjective. Some Neo pagans, wiccans and others call themselves witches and do not have a negative connotation about it. Others make a distinction : a witch is a spell caster who uses the power to do harm, or one that only uses the left hand black path, I really don't know a whole lot about it myself, but it is rather subjective and means different things to different people.