Non-denominational Muslims are Muslims who adhere to a form of Islam that is not restricted to any specific denomination. Such Muslims may choose to interpret the Islamic scripture, including the Quran and Hadith, themselves or consider the opinions of as many schools of Islamic thought as possible before reaching a particular interpretation.
In Arabic, they may be referred to as ghayr muqallids or ghair muqalideen (غير مقلّدين) while they have also been called nonconformists and its doctrine has been termed ghayr muqallidism. Such Muslims may defend this stance by pointing to the Quran such as Al Imran verse 103, which asks the Muslims to stay united and not to become divided. The term ghair muqallid literally refers to those who do not use taqlid and by extension do not have a madhab. In surveys asking for individuals to specify their religious denomination, such Muslims commonly self-identify as "just a Muslim". 
It has been described as a phenomenon that gained momentum in the 20th century which can overlap with orthodox Sunni tenets despite adherents not adhering to any specific madhab. In an alluding commentary on surah Al-Mu'minoon, verse 53 Abdullah Yusuf Ali states:
The people who began to trade on the names of the prophets cut off that unity and made sects; and each sect rejoices in its own narrow doctrine, instead of taking the universal teaching of unity from Allah. But this sectarian confusion is of man's making. It will last for a time, but the rays of truth and unity will finally dissipate it. Worldly wealth, power and influence may be but trials. Let not their possessors think that they are in themselves things that will necessarily bring them happiness.