This is the 3338th most frequent Arabic word.
شب
"شب" in Arabic means "youth" or "young man."
Here 'شب' is used as a noun, meaning 'young man', indicating a male in the youth age period.
رأيت شباً يلعب في الحديقة.
I saw a young man playing in the garden.
In this sentence, 'شبّ' is used as a verb, meaning 'to grow into adolescence or youth'.
شبّ الطفل عند دخوله المدرسة.
The child grew into adolescence when he started school.
Here, 'الشّبَ' refers to 'alum', a compound used in water purification and is a different usage entirely.