Sith Witch (Title Clarification)

In the story of Star Wars there have been instances where the specific sith female was considered a "Sith WItch." However there have also been instances where the sith female was just a sith. Now my question is... is "Sith Witch" an actual title bestowed upon certain sith females that have done an x achievement or is "Sith Witch" a general term for all sith females? Also any other terms and info about the title would be most helpful.