This is the 5368th most frequent Arabic word.
حاج
Pilgrim (specifically one who has performed the Hajj pilgrimage).
Here, 'حاج' refers to a person who is performing or has performed the pilgrimage (Hajj) to Mecca, which is a religious duty in Islam.
ذهب الحاج إلى مكة المكرمة.
The pilgrim went to Mecca.
In this context, 'حاجاً' is used to describe the person actively engaging in the activities of pilgrimage.
رأيت حاجاً عند المسجد يحمل زاده.
I saw a pilgrim at the mosque carrying his provisions.
Here, 'حاج' is used as an honorific title given to someone who has completed the pilgrimage to Mecca.