Shirk (شرك širk) in Islam is the sin of idolatry or polytheism (i.e., the deification or worship of anyone or anything besides God). Islam teaches that God does not share his divine attributes with anyone. Associating partners with God is disallowed according to the Islamic doctrine of Tawhid (oneness). Mušrikūn مشركون (pl. of mušrik مشرك) are those who practice shirk, which literally means "association" and refers to accepting other gods and divinities alongside God (as God’s "associates"). The Qur'an considers shirk as a sin that will not be forgiven if a person dies without repenting of it.
The word širk comes from the Arabic root Š-R-K (ش ر ك), with the general meaning of "to share".
In the context of the Quran, the particular sense of "sharing as an equal partner" is usually understood, so that polytheism means "attributing a partner to Allah". In the Quran, shirk and the related word mušrikūn (مشركون)—those who commit shirk and plot against Islam—often refer to the enemies of Islam (as in At-Tawbah verses 9:1–15).
According to the Encyclopedia of Islam, the Quran states "twice", in surah an-Nisa, verses 48 and 116, "that God can pardon all sins save one", that of shirk ("associationism").
Indeed, Allah does not forgive associating others with Him ˹in worship˺, but forgives anything else of whoever He wills. And whoever associates others with Allah has indeed committed a grave sin. —4:48
Islamic commentators on the Quran have emphasized that pre-Islamic Arabic idolatry invented a number of deities, most notable the three goddesses Manāt, Al-Lāt and Al-‘Uzzá, equal associates of God (as the Quran discusses in the 53rd surat) and the word mushrikūn (singular: mushrik) is often translated into English as "polytheists".
Entities worshipped besides God are called shuraka.. After Judgement Day, they will be cast into hell along with shayatin (satans) and evil jinn, to whom the pagans are also said to sacrifice in order to gain protection.