Having distinguished Brahman from the deity Brahma, the more substantial question the short disambiguation entry leaves untouched is what Brahman itself is said to be, and the central distinction Vedanta draws is between nirguna Brahman, without qualities, and saguna Brahman, with qualities.
Nirguna Brahman is Brahman considered in itself, prior to any attribute or relation: not merely without bad qualities but without qualities of any kind, since any positive attribute would, on the strict Advaita reading, introduce a distinction that would compromise its absolute unity. This is the Brahman approached through negation, the method of neti neti discussed elsewhere in this collection, and through formulas like sat-chit-ananda that point toward rather than describe. Saguna Brahman is the same reality as it appears to ordinary experience and devotion, a personal creator and object of worship, associated in different traditions with Vishnu, Shiva or the Goddess as the qualified form under which the ultimate is approached.
Shankara's Advaita treats nirguna Brahman as the final truth and saguna Brahman as a provisional accommodation, useful for minds not yet ready for the unqualified truth but ultimately transcended once liberating knowledge is attained. The theistic Vedanta schools reverse the emphasis: Ramanuja's Vishishtadvaita and Madhva's Dvaita hold that the qualified, personal Brahman is the final reality, and that Advaita's nirguna Brahman is at best a misleading abstraction from what a personal God actually is. The distinction restates the central and unresolved argument among the Vedanta schools that recurs throughout this collection: whether ultimate reality is a person to be loved or an absolute to be realized.