What is meant by the major ablution (al-wudu' al-akbar)? And how does a menstruating woman perform ghusl when she becomes pure?

The phrase "major ablution" (al-wudu' al-akbar) does not exist in the terminology of Islamic jurisprudence. Ablution (wudu') is purification from minor impurity (al-hadath al-asghar), while ritual bath (ghusl) is purification from major impurity (al-hadath al-akbar). It seems that some people use this phrase to refer to ghusl, and the ghusl from menstruation is the same as the ghusl from janabah (major ritual impurity).