What does "proof of reserves" and "proof of liabilities" mean? What is a brief way of describing what proof of reserves and proof of liabilities mean?
What is their difference? 

I have searched and read but I haven't got it yet.
Is it done by an auditor? Is it an audit?
Proof of reserves: This is proof that you actually control at least a particular amount of particular assets.

Proof of liabilities: The is proof that you do not owe more than a particular amount of particular assets.

So, for example, if an exchange can prove that it has reserves of 15,000 Bitcoins and that its owes its customers no more than 14,500 Bitcoins, then it has proven that its Bitcoin holdings are solvent.