Nirguna Brahman, is God without form in Hinduism. Even that definition is limiting. Nirguna Brahman is God, which is beyond human comprehension. For human eyes, Nirguna Brahman is viewed as Saguna Brahman, or God with personal attributes, and is commonly worshipped as Vishnu or Shiva by Hindus.
see also Parasiva; Mahavishnu
