What is the maximum duration of a menstrual period, is excess bleeding considered metrorrhagia (istihadah), and is it permissible for a husband to have intercourse with his wife during metrorrhagia?

Women, concerning menstruation, are divided into two categories: the beginner (mubtada'ah) and the habitual (mu'tadah). The beginner: her menstrual period is a maximum of fifteen days, and anything beyond that is irregular bleeding (istihadah). The habitual: her menstrual period is the duration of her customary period that she knows. If the continuous bleeding exceeds the majority of her customary days but does not exceed fifteen days, then it is menstruation; otherwise, it is irregular bleeding. A woman experiencing irregular bleeding is subject to the rulings of women in a state of purity regarding the obligation of prayer and fasting, and it is permissible to have intercourse with her.