Leviticus 15:25

But a woman who hath a defluxion of blood three days beyond the time of her separation, or when it floweth after the days of her separation, all the days of the uncleanness of her defluxion shall she be unclean; he who lieth with her shall be unclean.

many days, outside of her period of separation every woman has regular periods. This verse also describes a woman who suffers a constant flow immediately after her usual separation.

בלא עת נדתה, after the days of her menstruation have passed, as explained in Niddah 73 A woman is not described as being a zavah so that she would have to bring an offering after being healed unless the seven days during which she was a menstruant or expected to be a menstruant have passed. If after that period during the next 11 days she sees the symptoms of a zavah for three consecutive days she will require to count seven consecutive days during which she is free of these symptoms in order to be able to become ritually pure again. On the eighth day she is ready to offer her two bird offerings, one as a sin offering the other as a burnt offering.

זוב דמה,ואשה כי יזוב, “and if a woman have an issue of her blood, etc.” what is described here is what Solomon in Kohelet 10,18 alluded to when he said: בעצלתים ימך המקרה, “through slothfulness the ceiling sags, and through idleness of the hands, the house leaks.” The symbolism contained in this verse refers to the neglect by a woman in observing the laws of ritual purity, especially those laws involving menstruation. If the woman fails to examine herself before the onset of her menses this can have dire consequences, both for herself and the husband with whom she entertains marital relations. In the Talmud tractate Shabbat second chapter, death in childbirth by a woman is mentioned as one of these consequences. If she handled certain hallowed foods while in a state of ritual impurity, she made these foods unfit for consumption and conferred ritual impurity on the party handling them without even having eaten them. An interesting story on this subject is related in the Talmud, tractate, Niddah, folio 6. The famous Rabbi Gamliel had a servant woman working for him, who would regularly be required to seal caskets of wine [of a highly consecrated level, Ed.] and move them to another. After each single time she had moved them, she examined herself about whether her menses had begun, as otherwise the whole casket and its contents would have been unfit for further use. This servant maid found that after she had moved the last casket she had started her period. Upon telling this to her master, she was told that if she had not been in the habit of checking herself after each time she moved a casket, not only the last one but all of them would have become ritually contaminated. This is also why on folio 13 of the same tractate, we have a statement to the effect that anyone who makes a point of frequently checking herself out in this respect is especially praiseworthy.