The projects under this heading have generally been defined and may have had some (or even a significant amount of) work done on them. They may have assignments, but they haven't been touched in a while. In general, when the efforts on planned or ongoing project are ceased because of competing priorities, peopled have moved onto other tasks, etc. and the project page still exists, we use this collection to archive the project page. It's possible that people working on the project may return and move this back into the list of active projects or you may decide that you want to take on the project where they left it, assign yourself (or yourselves) and move it under active projects. If nothing else, you may find ideas or prior work in an uncompleted/abandoned project that is helpful to you or to the community in other ways.
If you would like to work on an abandoned project, contact the persons previously involved with the project and/or ask about it on OpenMRS Talk.