The Tractate Niddah is the only tractate in the Order of Taharot that contains both Mishnah and Talmud. As its name indicates, the major focus of this tractate is to clarify the laws of the niddah (a woman in menstruation.) These laws are the basis for taharat mishpacha (family purity) and the regular use of the mikveh in Jewish married life.

The final lines of the tractate elaborates on one of its main themes — the difference between a zavah and a menstruant. Both are conditions that require ritual purification but have different laws applicable to them.

Finally, the Talmud shares an Aggadic teaching about the importance of studying halachah (Jewish law) everyday:

Said R. Shmayah to R. Abba, "Might it be suggested that on account of a discharge in the day time a woman is a zavah, and that on account of one in the night she is a menstruant?"

"For your sake," the other replied, "Scripture (Leviticus 15:25) stated, 'By the time of her menstruation,' implying a discharge close to the time of her menstruation. Now which is a discharge that is close to the time of her menstruation, one that occurred in the night; and yet Scripture called her a zavah."

The school of Elijah teaches: Whoever repeats halachahs [ie: one who studies Jewish law] every day may rest assured that he will be a denizen of the World to Come, for it is said, "Halichot — the world is his." Read not halichot (goings) but halachot (laws).