Al-Istiahdah is when a woman’s bleeding does not cease.

It was narrated from Fatimah bint ani Hubaish that she suffered from Istihadah and the Messenger of Allah said to her: “If it is menstrual blood then it is the blood that is black and recognizable, so stop praying, and if it is other than that then perform Wudu’, for it is just a vein.” (Al-Nasa’i, declared sound by Al-Albani)