In the Bible, there are rules about things that will cause a person to be pure or unpure; clean or unclean, before Yahweh. The laws of clean and unclean tell us what is acceptable and unacceptable to our Heavenly Father, whether it be:
by food (Leviticus 11:1-47);
by childbirth (Leviticus 12:1-8.);
by the leprosy of man and of garments and of houses (Leviticus 13:1-59, Leviticus 14:1-57);
by issues (Leviticus 15:1-33).
The literature in this category covers these things.