Nidda is a term in Jewish law that refers to a woman during her menstrual period. According to Halacha, the Jewish legal system, a woman is considered a Nidda from the onset of her menstruation until she completes a ritual purification process. This period is significant in Jewish family life, as it affects marital relations and certain religious practices. During the Nidda period, couples typically refrain from physical intimacy. After the menstrual cycle ends, the woman must immerse herself in a mikvah, a ritual bath, to regain her status of purity. This practice emphasizes the importance of spiritual and physical cleanliness in Judaism.