The question you ask goes beyond popular science's understanding and field.
From what I gather and conclude. Those who are the most convinced they know the answer to that question, swear they have had spiritual experience in a realer than real environment at a time when their physical body was out of commision.
The key for knowing what consciousness really is, so far has always involved intuitive open mindedness based on collected information.
One who does not believe the consciousness cannot exist without the brain most likely will never begin to understand what it really is, until it's time for them. That in itself is debatable, and in that regard, if the consiousness really is rendered by the brain, then you'll already have your answer. Feeling that it's not rendered by the brain is an interesting step.
In short, if I were to add my input as to what consciousness truely is, it would draw much doubt from those who on the most part adopted someone elses theory, or couldn't possibly take the time to make sense of whatever reasoning one like myself would deliver.