"What is X" simply means: "tell me everything i want to know about X".
Since that is usually a lot there is also an implicit "start with most important stuff" but the context can be even more discriminating as in "just tell me the size of it"
No. What is X, in terms of matter, is a question about essence, not features or behavior.
It is to take knowledge of matter to a point where there is nothing else to know.
There is nothing else to know but behavior. What do you suggest there should be? Meaning? Intention?