Is the white discharge (al-Qassah al-Bayda') the light yellowish discharge that appears in the last days of the menstrual period, or is it the abundant white discharge that follows it and continues for days?

The yellowish and brownish discharges connected to blood are considered menses, and one must abstain from prayer, fasting, and all other acts prohibited for a menstruating woman as long as these discharges are visible. As for the white discharges that follow, they are not considered menses. Upon the cessation of the yellowish and brownish discharges, a woman must perform ghusl (ritual purification bath) and is then considered pure, whether she sees white discharges or not.