The Qur'anic term for the 'opening chapter' of the Qur'an, which is also called 'Umm al-Kitab', is

Surah Al-Fatihah (Chapter 1) is known as 'Umm al-Kitab' (Mother of the Book) because it encapsulates the core themes of the entire Qur'an, including monotheism, worship, and guidance. It is the opening chapter of the Qur'an and is recited in every unit (Rak'ah) of the Islamic prayer. It is also called 'Al-Sab' al-Mathani' (The Seven Oft-Repeated Verses).