Western media, in its unrelenting agenda to demonise the faith and its adherents will have one believe it means- Islam's God is greater than other gods.
Essentially pitting people against one another.
Regular people would assume it means God is greater/bigger/ stronger than the biggest / strongest thing they can imagine.
Imam Ja'far Ibn Mohammed Al Sadiq (عليه السلام) so beautifully explains the meaning when he says:
الله أكبر من أن يوصف
Allah is greater than to be defined.
In other words, Allah Ta'ala, our Creator, (تقدست أسماؤه) in His majesty and glory transcends our limited intellect and our limited dimensions of space and time. He is beyond definition itself.
الله أكبر من أن يوصف
الكافي ج 1 ص 118
AlKafi- 1/118
وَفَوْقَ كُلِّ ذِي عِلْمٍ عَلِيمٌ
And above every man of knowledge is The All Knowing.
12.76