Working papers, sometimes called discussion papers, are papers which are still in progress and have yet been accepted for publication. Often scholars will post a working paper or present the work at a conference to solicit comments.
Working Papers are a form of grey literature, which means that they are not works which go through a commercial publisher. As the web becomes more of a repository for faculty papers, many faculty sites make this preliminary research more accessible, especially in economics, finance and law. Working papers are produced by researchers at universities, governments, ngo's, research organizations, think tanks or other professional organizations. Many post working papers on their own sites. There are also aggregator noncommercial websites which try to house this material. SSRN is probably currently the most recognizable of these networks. Databases like Business Source Complete and Econlit are beginning to index some of this material.