Brahman

Brahman (bráhman-, nominative bráhma ब्रह्म) is a concept of Hinduism. Brahman is the unchanging, infinite, immanent, and transcendent reality which is the Divine Ground of all matter, energy, time, space, being, and everything beyond in this Universe. The nature of Brahman is described as transpersonal, personal and impersonal by different philosophical schools. In the Rig Veda, Brahman gives rise to the primordial being Hiranyagarbha that is equated with the creator God Brahmā. The trimurti can thus be considered a personification of Hiranyagarbha as the active principle behind the phenomena of the universe. The seers who inspired the composition of the Upanisads asserted that the liberated soul (jivanmukta) has realized his identity with Brahman as his true self (see Atman (Hinduism)).
The word "Brahman" is derived from the verb brh (Sanskrit:to grow), and connotes greatness. The Mundaka Upanishad says:
Om- That supreme Brahman is infinite, and this conditioned Brahman is infinite. The infinite proceeds from infinite. Then through knowledge, realizing the infinitude of the infinite, it remains as infinite alone.
Note that "Brahman" is different from "Brahmin," the Priests/Holy Men. In fact Brahmin is derived from Brahman in the sense that a 'Brahmin is the one who knows Brahman'. The confusion between the terms can be dated back to the translation of the Upanishads into modern English.

http://en.wikipedia.org/wiki/Brahman