The word Brahman is derived from the Sanskrit word for power, specifically the power of ritual and sacrifice to change the material world. Hence, the secondary meaning of the word which refers to the highest caste of Hinduism, the Brahmins, who have such powers.
In the Vedantic schools of Hinduism, as found in the sacred writings of the Upanishads, the word refers to the ultimate, unchanging reality that lies behind all the objects and activities of the external world. It is composed of pure being and consciousness and to some extent may be called the "world soul."
Brahman is the source of the universe. Viewed as divine intelligence, it pervades all beings, including the individual soul. Thus the many Hindu deities are manifestations of the one Brahman. In the earliest religious texts, the Vedas, all the gods are seen as issuing from Brahman:
Philosophers of the Upanishads identify Brahman, the world soul, with atman, the inner essence of the human being, or the human soul. In the Hindu pantheon, Brahman is identified with Brahma of the Hindu trinity of Brahma (the Creator), Vishnu (the Preserver) and Shiva (the Destroyer).
While Brahman lies behind the sum total of the objective universe, the human mind boggles at any attempt to explain it with only the tools provided by reason. Brahman is beyond the senses, beyond the mind, beyond intelligence, beyond imagination.
'Brahman' is also an alternate spelling of Brahmin, the highest of the four castes, or 'varnas' in the Indian caste system.