Shirk

Shirk (شرك or širk) is the sin of practicing idolatry or polytheism, i.e. the deification or worship of anyone or anything besides Allah. Islamic scriptures say Allah will forgive every crime of Muslims but not shirk. Literally, this word means ascribing or establishing "partners" next to Allah. The meaning of this can be highly metaphorical; traditionally Muslims have accused Christians of shirk for ascribing a son to god, but modern salafis also accuse overly Westernized or non-observant Muslims of shirk over worshiping the "dunya" or world.