Laws of Impurity and Purity

In biblical terms, a Niddah is a woman experiencing a menstrual flow who is thus required to abstain from intimacy with her husband and renders impure items that are susceptible to ritual impurity. After the destruction of the Second Temple, the latter concern fell away and the term comes to refer also to an entire category of Jewish ritual purity law that governs the intimate relations between a husband a wife, also sometimes known as the laws of family purity. 

Taharah is ritual purity and contrasts to tumah, ritual impurity. While the Temples stood, one needed to be in a state of ritual purity to enter the Temple and offer a sacrifice. To attain such a status, depending on the nature of the impurity contracted, the purification process may have entailed a waiting period, sprinkling with the ashes of a red heifer, and immersion in a mikveh. Purity and impurity are the focus of Seder Toharot. While most of these laws are no longer observed in the absence of the Temple, some still are.

"Tumah" in Hebrew.

Tzara'at is a biblical disease that involved discoloration of one's skin, home, or clothing. Once confirmed by a priest's inspection, it renders the subject ritually impure, requiring them to leave the camp for a period, undergo further inspection, and then a purification process. Tzara'at is the subject of Leviticus 13–14. Several biblical stories have characters inflicted with tzara'at. And tzara'at is the subject of the Mishnah's tractate Negaim.

Zav is a halakhic term for a woman with a genital discharge.