Niddah (or nidah; Hebrew: נִדָּה) is a Hebrew term describing a woman during menstruation, or a woman who has menstruated and not yet completed the associated requirement of immersion in a mikveh (ritual bath).
In Leviticus, the Torah prohibits sexual intercourse with a niddah and the prohibition has been maintained in traditional Jewish law. The laws concerning niddah are also referred to as taharath hamishpacha (Hebrew for family purity).
Read more about Niddah: Etymology and Usage, Application of The Torah, Privacy of The Niddah Process, Academic Studies of The Extra Days, Niddah in The Conservative Movement, Extent of Adherence To These Laws