What is the meaning of the word "Al-Alameen" (the worlds) mentioned in the Holy Quran?

Al-ʿālamīn (with a fatḥah on the lām): This is a name for every existent being other than Allah the Almighty, based on His saying: "Pharaoh said, 'And what is the Lord of the worlds?' He said, 'The Lord of the heavens and the earth and whatever is between them, if you should be convinced.'" As for al-ʿālimīn (with a kasrah on the lām): this refers to the people of knowledge.