Short answer
Quran is an Arabic word meaning "the recitation" or "that which is read". It comes from the root qara'a, to read or recite. It is the name of the holy book of Islam, the words of Allah revealed to the Prophet Muhammad ﷺ through the angel Jibril.
Muslims of every school define the Quran as the speech of Allah revealed to the Prophet Muhammad ﷺ in Arabic, transmitted by mass narration (tawatur), written in the mushaf, and recited as an act of worship. Believing in it as the word of Allah is part of iman.
The four schools agree on this.
Explanation
The word Quran comes from the Arabic root qara'a, which means to read or to recite. Most scholars say it is a verbal noun meaning "recitation", used for the thing recited. The Quran uses the word in this sense about itself: Allah tells the Prophet ﷺ that it is upon Him to collect it in his heart and make possible its recitation, its qur'an (75:17 to 18). The very first word revealed was Iqra, "Recite" (96:1).
The name fits how the book lives: it is recited in every salah, memorised by millions and read aloud daily, not only kept on a shelf. The spelling Koran is an older English form of the same word; Muslims today usually write Quran or Qur'an.
Other names the Quran gives itself: al-Kitab (the Book), al-Furqan (the Criterion between truth and falsehood), al-Dhikr (the Reminder), al-Huda (the Guidance) and al-Nur (the Light). The physical written copy is called the mushaf.
So when someone asks what holy book Muslims follow, the answer is the Quran, together with the Sunnah of the Prophet ﷺ that explains it. The four schools agree on this definition. For an overview of the book, its structure and its history, see What is the Quran? and the history of the Quran.
The evidence
Quran, Surah Al-Qiyaama 75:17-18
إِنَّ عَلَيْنَا جَمْعَهُۥ وَقُرْءَانَهُۥ ﴿١٧﴾ فَإِذَا قَرَأْنَٰهُ فَٱتَّبِعْ قُرْءَانَهُۥ ﴿١٨﴾
Indeed, upon Us is its collection [in your heart] and [to make possible] its recitation. So when We have recited it [through Gabriel], then follow its recitation.
The Quran uses the word qur'an for its own recitation.
Quran, Surah Al-Alaq 96:1
بِسْمِ ٱللَّهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ ٱقْرَأْ بِٱسْمِ رَبِّكَ ٱلَّذِى خَلَقَ ﴿١﴾
Recite in the name of your Lord who created -
The first word revealed was the command to recite, from the same root as Quran.
Where the ruling is recorded
- Usul al-Shashi, Opening section on the Book of Allah. Hanafi usul text defining the Book as transmitted by mass narration and written in the mushaf.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.