العَالَمِيْنَ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – العَالَمِيْنَ is a noun

A noun may either be 1) Definite or indefinite 2) Masculine or feminine 3) Singular, dual or plural 4) Nominative, accusative or genitive

العَالَمُوْنَ is the natural state of this definite noun and it changes to العَالَمِيْنَ due to: 1) a preposition that precedes it or 2) a possessed noun that precedes it or 3) it’s a noun of dependent declension a) نَعْتٌ / صِفَطٌ adjectives b) التَّوْكِيْدُ emphatic c) المَعْطُوْفٌ conjunction d) البَدَلُ synonym

By means of which one knows a thing, hence it signifies worlds or creations, because by it the Creator is known (worlds signifies all categories of existence, both in the physical and the spiritual sense, known and unknown, all that is besides Allah (SWT) animate and inanimate, knowledge, science, learning, information) 

Grammatical analysis of العَالَمِيْنَ
اسْمٌ مَجْرُوْرٌ وَعَلَامَتُ جَرِّهِ اليَاؤُ لِأَنَّهُ جَمْعُ المُذَكَّرِ السَّالِمِ
Surah/Below are the 73 verses in the holy Quran containing the genitive nounالعَالَمِيْنَ
Verse
1-2Every form of praise and thanks belongs to Allah (SWT), Nurturer of all that existsالحَمْدُ لِلَّهِ رَبِّ العَالَمِيْنَ
2-47
2-122
2-131
2-251
3-33
3-42
3-96
3-97
3-108
5-20
5-28
5-115
6-45
6-71
6-86
6-90
6-162
7-54
7-61
7-67
7-80
7-104
7-121
7-140
10-10
10-37
12-104
15-70
29-15
29-28
32-2
37-79
37-87
37-182
38-87
39-75
40-64
40-65
40-66
41-9
43-46
44-32
45-16
45-36
56-80
59-16
68-52
69-43
81-27
81-29
83-6