If your "exhaustive reading" is in the context of research e.g. social science research, then "exhaustive reading" refers to reading existing / previous literature e.g. journal articles, theses etc pertaining to your research area continuously until the literature is saturated i.e. no more new discovery / insight you can extract from those literature reviewed.
Let me give you a scenario - after conducting literature review for a while, you found some new journal articles / theses that you haven't read and after you'd read them, you found no more new information / insight discovered from them indicating you have reached saturation or exhaustiveness in your reading. Normally we do this exhaustively / leave no stone unturned so that we don't missed out some important literature that article reviewers / theses examiners might question us in future. Wishing you all the best.
Thank you very much dear sir. Would you please give me the exact reference of the definition of "exhaustive reading" or any reference of book to read further.