ad-Dīn is interpreted in five senses:
1. ad-Dīn is used in the sense of tawhid (the oneness of God); as in the following verses:
Indeed, the religion {that is, tawhid} in the sight of Allah is Islam. (Āl ʿImrān 3:19)
So worship Allah, [being] sincere to Him in religion {that is, in tawhid}. (az-Zumar 39:2)
This is also the case in similar commands in the surahs of Luqmān, ar-Rūm, and others.
And when they board a ship, they supplicate Allah, sincere to Him in religion {that is, in tawhid}. (al-ʿAnkabūt 29:65)
There are many similar verses.
2. ad-Dīn is used in the sense of reckoning/account; as in the following verses:
Master of the Day of Judgment {that is, the Day of Reckoning}. (al-Fātiḥa 1:4) This is the Day of Judgment {that is, the Day of Reckoning}. (aṣ-Ṣāffāt 37:20)
Those who deny the Day of Judgment {that is, the Day of Reckoning}. (al-Muṭaffifīn 83:11)
Will we indeed be brought to account {from the root dīn, madīnūn}? (aṣ-Ṣāffāt 37:53)
If you will not be brought to account [from the root dīn, madīnīn]... (al-Wāqiʿa 56:86)
3. ad-Dīn is also used in the sense of judgment/ruling; as in the following verses:
The [unmarried] woman or [unmarried] man found guilty of sexual intercourse—lash each one of them with a hundred lashes, and do not be taken by pity for them in the religion of Allah {that is, in applying Allah's ruling concerning the adulterer}. (an-Nūr 24:2)
He could not have detained his brother under the king's law {that is, according to the king's judgment and ruling}. (Yūsuf 12:76)
4. By ad-Dīn, the institution by which the servants obey Allah, i.e., religion, is meant; as in the following verse:
It is He who sent His Messenger with guidance and the religion of truth {that is, the religion of Islam} to make it prevail over every [other] religion {that is, to make the religion of Islam, which is followed in obedience to Allah, prevail over other religions}, although those who associate others with Allah dislike it. (at-Tawba 9:33)
A similar verse is also found in Saff.
It is He who sent His Messenger with guidance and the religion of truth {that is, the religion of Islam} to make it prevail over every [other] religion {that is, to make the religion of Islam, which is followed in obedience to Allah, prevail over other religions}. (al-Fatḥ 48:28)
5. ad-Dīn is used in the sense of nation [religion and sharia]; as in the following verse:
Inclining toward truth, the religion of Abraham... (Āl ʿImrān 3:95)