The word “Brahman” is stated in many verses of the Bhagavad-Gita and other scriptures. It is important to understand the terms used.
What is Brahman?
“The Supreme Personality of Godhead said: The indestructible, transcendental living entity is called Brahman…” (Lord Krishna, Bhagavad-Gita 8.3)
So basically we, the living entity (the souls) are known as Brahmans.
What is Para Brahman?
Lord Krishna is Para Brahman (Supreme Brahman), also addressed as Paramatma (the supersoul within all bodies).
Sanskrit of Bhagavad-Gita 10.12: Param Brahman
English translation: Supreme Personality of Godhead
“The living entities in this conditioned world are My eternal fragmental parts…” (Lord Krishna, Bhagavad-Gita 15.7)
Since Lord Krishna is the Supreme Brahman, we (the souls) are Brahman, because we are part of Lord Krishna.
Note: Brahmanda means universe.