Niddah (or nidah, nidda, nida; Hebrew: נִדָּה‎) is a Hebrew term which literally means separation, and generally refers to separation from ritual impurity; The term niddah is overwhelmingly used in Judaism to refer to the rules of Jewish law concerning menstruation. In common usage, a woman is said to be a niddah when she is menstruating, or has menstruated without yet completing the associated ritual requirements.