Assalamualaykum, What is the major impurity in Islam? If I don’t know what the major impurity is and I still do ghusl intending to remove major impurity (without knowing what major impurity is). Will this Ghusl be valid and can I pray after that? JazakAllah Khair.

major ritual impurity (Hadath Akbar) is what requires a full ritual bath (Ghusl), such as Janabah, menstruation, and postpartum bleeding. If someone performs Ghusl with a general intention—such as "lifting the major impurity" or "making prayer permissible"—their Ghusl is perfectly valid. Their state of impurity is lifted, and they are permitted to pray. Furthermore, I would like to clarify that having a precise, technical understanding of the exact nature of the impurity is not required for this intention to be valid.