It has been said that there is nothing in Hinduism more mysterious than Brahman. It is not a physical entity that you can point to, touch, or smell. The term “Brahman” means “the one without a second” or “the one that is multiple.” Unlike Brahma, Brahman is not a personal, creator god.
Yet the term Brahman is essential to Hindu metaphysics. Brahman is the divine force that sustains the entire cosmos or world order. The stage for Brahman is the Upanishads, where it is exalted above all other forms of god. Brahman is an absolute godhead — infinite, changeless, and impersonal.
The term “Brahman” was developed in the Upanishads to mean “the All” or “ultimate reality.” Even each individual self or atman is identical to the Brahman. Interestingly, the different views of Brahman were both theistic, in which it is identified with a god or goddess, and nontheistic, in which the Brahman was seen as a reality that lay beneath everything else.
Brahman is often understood via illustration. Here a sage explains to a student the ultimate nature of reality.
No one can understand the sound of a drum, without understanding both the drum and the drummer. No one can understand the sound of a conch shell, without understanding the shell and the one who blows it. No one can understand the sound of a lute, without understanding both the lute and the one who plays it. As there can be no water without the sea, no touch without the skin, no smell without the nose, no taste without the tongue, no sound without the ear, no thought without the mind, no work without the hands, and no walking without feet, so there can be nothing without the soul.
When you throw a lump of salt into water, it dissolves; you cannot take it out again, and hold it in your hands. Yet if you sip any part of the water, the salt is present. In the same way the soul can be perceived everywhere and anywhere; the soul has no limit or boundary.
At present there is a duality. ‘You perceive other beings: you see them, hear them, smell them, and think about them. Yet when you know the soul, and when you recognize that the soul within you is the soul of all beings, how can you perceive other beings? How can you see and hear them, smell then and think about them? How can you regard yourself as subject and other beings as objects, when you know that all are one?’
— Brihadaranyaka Upanishad 1:4.1–4, 8
In the Upanishads, Brahman is the Absolute One, the ground of all being which makes all things known. According to Advaita (nondual) philosophy, Brahman alone is real; to see duality is unreal or maya.
Advaita is a term used to describe the unitary philosophies and religious movements in India. Instead of describing these schools as being unitary or monistic, a negative term is employed. Thus, advaita is usually translated as “nondual.” Duality would imply that there is more than one reality; nonduality implies that there is only one reality.