Brahman is undefinable

The entire visible world, including mind, intellect, actions, Iswar, etc., disappear at the final ending of the Great Period (maha kalpa), i.e. at the time of Great Dissolution (maha pralaya). Space and time also become extinct at that position. The immutable substrate Brahman only will remain. It is not time, space, the five fundamental elements or any other thing. We cannot describe or define what it is. Only Knowers of Self can understand It. The rest of the folk has to take recourse to Vedic aphorisms to talk about it.

YOGA VAASISHTA – Part Vl, Nirvana (Liberation), Book ll, transl. Dr. Vemuri Ramesam