المعنى الاصطلاحي :

Major issues of the religion that a Muslim is not excused for not observing, regardless of whether they are matters related to belief, statements, or actions.

الشرح المختصر :

"Usool" (fundamentals): The components of the religion of Islam are not of the same level. It has "usool", which are called "usool-ud-deen" (fundamentals of the religion), and it also has sub-issues, which are called "furoo‘" (branches). The "usool" constitute the major issues that pertain to theory, including the issues of monotheism, divine attributes, predestination, prophethood, and the Hereafter, or that pertain to practice, such as the pillars of Islam, including the prayer, fasting, pilgrimage, Zakah, etc.

التعريف اللغوي المختصر :

"Usool" (sing. asl): the bottom of something. Original meaning: foundation upon which something is built. Other meanings: the first, the pure, the origin.