Brahman literally means the vast, the infinite. What is it? It is awareness and infinite existence,. Awareness itself is called another bliss. And that thou art, you are that. This is called brahman. Atman alone is real. Everything else which you are seeing is not separate outside the atman. The entire universe is an appearance in you. Just like movies are an appearance in the screen. They are nothing apart from the screen. So thi entire universe has no existence apart from the consciousness.