In the Upanishads, Brahman is used to sometimes refer to The Fabric of Consciousness, and sometimes to an instantiated/incarnated monad, or Spiritual Ego (i.e. Brahman entering the body, for e.g., in the Taittirya Upanishad).
" Brahman connotes the highest Universal Principle, the Ultimate Reality in the universe. In major schools of Hindu philosophy, it is the material, efficient, formal and final cause of all that exists. It is the pervasive, genderless, infinite, eternal truth and bliss which does not change, yet is the cause of all changes. Brahman as a metaphysical concept is the single binding unity behind diversity in all that exists in the universe. ..The Vedas conceptualize Brahman as the Cosmic Principle. In the Upanishads, it has been variously described as Sat-cit-ānanda (truth-consciousness-bliss) and as the unchanging, permanent, highest reality."
"Brahma (ब्रह्म) (nominative singular), root bṛh-, means "to be or make firm, strong, solid, expand, promote."
The term may also refer to someone who has knowledge/experience of Brahman (a brahmin priest (The Unfolding and its source.
Brahmana (ब्रह्मण): A brahman priest, one who has knowledge of Brahman, related or given by Brahman.