2,070. Zivah Blood

Hilchos Issurei Biah 6:2

Pursuant to the previous halacha, if a woman menstruates for the first time or if she menstruates at her regular time, she is rendered a niddah for seven full days. This is so regardless of whether she keeps on bleeding throughout the seven days or whether she only found a single drop of blood. If she finds blood on the eighth day, it is zivah blood because it came outside of the time for her niddah.

Hilchos Issurei Biah 6:3

Any blood found between one time that a woman is expected to menstruate and the next is zivah blood. It is a law communicated to Moses at Sinai that there aren’t more than eleven days between one menstrual period and another.