1. what does the word “Esoteric” mean?

The origin of the word “Esoteric” is Greek, it means the hidden and private: “the teachings that are hard to grasp by those who are not intellectually illuminated” as mentioned in the Larousse Dictionary, and “the sciences of the elite” as mentioned by Britanica. As to the Arabs, they described it as “the science restricted to those who can understand it” As to our books, they unfold the secrets of these special sciences and present them in a simplified way which is within the reach of understanding by everyone.