What does “WP” mean?
A workprint is a copy of the film that has not been finished. It can be missing scenes, music, and quality can range from excellent to very poor. Some WPs are very different from the final print, and others can contain extra scenes. Workprints can be nice additions to the collection once a good quality final has been obtained.
For example, the “Men in Black” workprint is missing all the aliens, and has actors in their places. A recently leaked workprint was the one for X-Men Origins: Wolverine, in which many of the special effects had not yet been added. This release was made available long before the film was to be released.