Nirguna Brahman, (Devanagari निर्गुण ब्रह्म, nirguṇa brahman, the supreme reality without form, quality, attribute) signifies in Hindu philosophy the Brahman that pervades the Universe, considered without form (guna), as in the Advaita school or else as without material form, as in Dvaita schools of philosophy.
According to Adi Shankara, the famous reviver of Advaita Vedanta, the nirguna brahman is non-different from the supreme personality, God, whatever qualities we attribute to the divine. By the power of Maya (illusion) the supreme lord (Ishwara) playfully creates multiple worlds and deludes all beings, who are in essence non-different from Him. This world is only relatively real and the real self is not affected by it. The lord appears time and again in this world to show the path of liberation: He seems to take birth but that is an illusion because He is birthless. His body is transcendental, unlike our bodies which are created and destroyed. One can worship Him as one's own self or as (fully or partially) distinct from oneself. If one worships any deity one will reach the world of that deity (Hiranyagarbha) but, perhaps after millions of years, deity and devotee will reach para vasudeva or "beyond the divinity". The desireless soul can reach this state here and now: this is called Jivanmukta or "free while alive". This school essentially advocates God as being immortal and formless.
Read more about this topic: God In Hinduism