"What is consciousness?"
How do we answer such a question? The same way we answer any question in the form "what is X". And there are only two ways to answer those types of questions:
a) With a tautology. Example: "what is velocity?" - "velocity is change in position with time". Except as exercises in logic, tautological answers are meaningless, in the sense that they do not tell you anything you don't already know.
b) With a reference to a larger, less specific category. Example: "what is a cat?" - "a cat is a feline", "a cat is a mammal", "a cat is an animal", ..., "a cat is a thing". The less specific the category referenced in the answer, the less meaningful it becomes. "Cats are felines" is certainly more meaningful than "cats are things", but still there are far more things that are true about cats than things that are true about felines, so the answer may not be satisfying.
I can't think of any other way to answer a "what is..." question. And if there is no other way, that means those questions don't have meaningful answers that are true! If you start with a "type b" kind of answer, the more you refine it so as to make it more true while remaining meaningful, the more it will look like a tautology. If you start with a "type a" answer, the more you try and generalize to make it more meaningful, the less true it becomes. Just look at the answers on this thread so far!
Obviously the point of answering a "what is X" question can't possibly have anything to do with knowing meaningful truths about X, since a meaningful, true, and non-tautological definition of X simply does not exist. So why do we ask?
And therein lies the answer. In order to know the best answer, you have to understand why you are asking a question that has no answer. If you're interested in controlling the object of your question, then you must seek for a "type b" answer. That is what scientists do; they come up with false answers which nevertheless give them some power over the objects they study. On the other hand, if you're interested in the truth, you must necessarily find a "type a" answer. Tautologies are useless, but they do give us a sense of intellectual accomplishment.
Here's what I think about consciousness:
type a: consciousness is our ability to obtain knowledge about anything including ourselves
type b: consciousness is a self-referent language
Have fun-