On the 'Amulet of Samurkand' book, there is somthing which is called the '7 planes'. What does this mean?

Question

To whoever reads it.

Answer 1

They are differet "planes of being/existence"

"Nathaniel commands Bartimaeus to steal the Amulet of Samarkand from Simon Lovelace, a task that the djinn completes with some ease. Other factors quickly become more interesting: the motive for the boy's charge, how Simon came by the Amulet and the fallout from the theft. What these reveal about the characters of Simon and Nathaniel makes for engrossing reading. Stroud also introduces the fascinating workings of the 'seven planes' (magicians can see three of them only with special spectacles), the pecking order of magical beings, and the requirements of various spells and enchantments — plus the intrigue behind a group of commoners mounting a Resistance (this loose end, presumably, will be explored in the remainder of the planned Bartimaeus trilogy). "

"I love footnotes in fiction -- and The Amulet of Samarkand is full of them. This is because the Djinni Bartimaeus is so brilliant he can think and see on seven planes of existence at once, while all he can do to simulate that experience for the reader is to footnote. That Bartimaeus even exists in the first plane is due to an unhappy magician's apprentice named Nathaniel."

Answer 2

A reference to the Sufi(which is a branch of the Islamic Religion)understanding of Human existence.Sab’a Samawat (The Seven Skies)or Seven Planes.
Similar to the Seven Valleys in the Bahá'í Faith, these are the boundaries of the material Realm. The seven skies can be thought of as 7 energy levels or 7 levels of enlightenment ,which surround our world.At the end of 7th sky is the height known as the Baitul Mamoor (Inhabited Dwelling) . After which lies the station which is called Sidratul Muntaha (Lote Tree), which is the last limit of the flight of the most intimate angels.
Sab’a Samawat (The Seven Skies)
Similar to the Seven Valleys in the Bahá'í Faith, these are the boundary of the material Realm. The seven skies can be thought of as 7 energy levels or 7 levels of enlightment . At the end of 7th sky is the height known as the Baitul Mamoor (Inhabited Dwelling) . After which lies the station which is called Sidratul Muntaha (Lote Tree), which is the last limit of the flight of the most intimate angels.