ASSALAM O ALAIKUM!
Heaven: The word “Jannah” has been derived from the word “Jann” which means “to hide something”.
Jannah (Heaven) is so called because its land has been hidden by the dense gardens & orchards.
According to Hazrat Ibn-e-Abbas رضی اللّہ تعلا عنہ , The word “Jannah” is in plural terms because there are seven (7) Heavens:
According to Mo’az Bin Jabal رضی اللّہ تعلا عنہ , Muhammad صل اللّہ علیہ وسلم said: “Verily, there are 200 Levels (دراجات) in Heaven & there is the distance of Earth & Sky between two of the consective levels. The highest grade is in Jannat-ul-Firdaus, above which is Arsh of Rehman & the Rivers of Jannah originate from this place. Thus whenever you raise your hands, pray for Jannat-ul-Firdaus to Allah عزوجل. (Trimidhi)
Any mistake, on my part, if found, may please be forgiven.