Nirguṇa Brahman is the absolute considered without any attribute. For Advaita Vedānta this is Brahman as it truly is: undivided consciousness of which nothing can be predicated, approached only by negation. Every description, even that of a personal God, belongs to the level of appearance. Other schools of Vedānta reject the idea that the highest reality lacks qualities.
Nirguṇa Brahman
Brahman “without qualities”: the absolute as it is in itself, beyond every attribute, name and form.
Also: Nirguna Brahman