From Georgia Tech Library:

What are conference proceedings?

Conferences are a major source of cutting edge research, particularly in science and engineering. At conferences, researchers present papers on the research they are doing and obtain feedback from the audience. The papers presented in the conference are then usually published in a volume called a conference proceeding. It may be months before such information is published as a journal article, or it may never be published.

Why are conference proceedings hard to find?

Publishers are inconsistent in how they publish proceedings. Sometimes the proceeding is treated like an individual book.  In other cases a conference that occurs every year or so may be treated like a journal, so that there is only one library catalog record for all the years of that conference's proceedings. Sometimes the papers from a conference are not published and may only be available from the authors. All of these factors combine to make conference papers and proceedings difficult to find. The most important thing to remember is that if you have any difficulty finding a conference proceeding or paper, please ask a librarian for help.