Niddah (or nidah, nidda, nida; )'s a Hebrew term which literally means separation, and generally refers to separation from ritual impurity; The term niddah's overwhelmingly used in Judaism to refer to the rules of Jewish law concerning menstruation. In common usage, a woman's said to be a niddah when she's menstruating, or has menstruated without yet completing the associated ritual requirements. Meaning and use of the term The term niddah appears in the biblical description of the red heifer… (More on Niddah)