The Essence
Al-Jaleel refers to the absolute majesty, glory, and awe-inspiring greatness of Allah's attributes. His majesty is so overwhelming that nothing in creation can fully encompass or comprehend it.
In the Quran
وَيَبْقَى وَجْهُ رَبِّكَ ذُو الْجَلَالِ وَالْإِكْرَامِ
"And there will remain the Face of your Lord, Owner of Majesty (Al-Jalal) and Honor. (Surah Ar-Rahman 55:27)"
In Your Duas
يَا ذَا الْجَلالِ وَالإِكْرَامِ
"O Owner of Majesty (Jalal) and Honor."
— Sunan at-Tirmidhi 3524 (Prophetic recommendation to use this phrase often)