Classical Chinese is the language of Ancient Chinese literature and philosophy. It is the written language in which the texts of Confucius, Laozi, Mengzi, Sun Tzu and many others were written. This language roughly corresponds to the Old Chinese that was spoken at the time.
Eventually, Classical Chinese would become Literary Chinese, as the written language diverged from the oral language. This language conserves a similar written structure to Classical Chinese, but starts to diverge in some aspects. Literature like the Tang poems and the great novel Romance of the Three Kingdoms are written in literary Chinese, at least in part in the case of the latter.