Nunation (تنوين) in Arabic is used when there is no definite article ال. But that is only half of the truth. The idea is much deeper.
Nunation (تنوين) can tell you something about the character and personality of a word. It is a deep idea developed by the first Arab grammarians.
Hard to imagine today, but the grandmasters of Arabic grammar were superstars during their lifetime. Here is a list of the TOP 5 Arabic grammarians of all time.
The question of the wasp or hornet - Masʾala(t) al-Zunbur (مَسْأَلة الزُّنْبُور) - caused Sibawayhi, the most famous Arabic grammarian, to die of anger.