The main purpose of the article, as the topic itself shows, is defining an eternal GEOMETRY(as a basic foundation and unavoidable structure)for the Islamic architecture. Therefore, as an abstract of this article, (giving a short but conclusive definition of the main subject),and in order to avoid from some possible misunderstandings in the mentioned subjects and meanings in the article, the following points seems to be useful:A. The referring meaning of the word "GEOMETRY" (or its Arabic synonym "Hindiseh") by the author in this (article) is completely different from the common meaning of it in architecture (or the Euclidian GEOMETRY) and its closed and limitful field of rules of some mathematical meanings and physical shapes and forms. But by the phrase "Hindiseh Jaavidan" or "Eternal GEOMETRY" the author means the Unique, Wholistic and Comprehensive Truth, which according to the Quranic literature, is known by some Arabic terms such as "qadr", "taqdeer" and "muqaddir", "muqaddar", "qadeer", and so on. The meaning which points to the comprehensive and wholistic system of rules governing all various systems of measurement essential for the whole universe and its every individual parts's or thing's coming into existence (in their both physical being and meaningful identity).B. According to the above mentioned description, the referring meaning of the phrase "Natural GEOMETRY" (or "Hindisi-yi Tabee 'at" or "Taqdeer") by the author in this article can be imagined as a symbolic light through which everything in the universe become visible, readable and understandable for every other thing in the whole cosmos of varieties and multiplicities (in both qualitative and quantitative groups of limits and measures). The limits and measures without which everything's essential mutual relation and harmonic suitable cooperative sharing life with every other thing in the world seems to become impossible.C. Then, in a similar symbolic structure, the other important meaning of "GEOMETRY" or "Hindisih" to which the author is going to point to is "The Essential GEOMETRY" or "Hindisik-yt Dhaatee". According to the Holy Quran, for every possible matter of being in the physical world, there is a limitless, unchangeable, eternal specific and determined Truth in The Presence of God which, as same as all other Truthful Meanings in such a Sacred Presence is free from all limits essential for the material world such as: matter, physical shape and form, length, width, thickness, color and other similar limits.D. And at last, the author's purposed meaning of the subject of "Islamic Architecture" in this article, is an orderly and unitary structure which in its both whole and parts, and in its both physical structure and meaningful identity obey the One Divine System of Rules named Islam. And, at last, by the word of "Islam" means the universal governing order of both physical and spiritual worlds.