"Shelving a project" is like deleting a project into a recycle bin. When you shelve a project, it'll disappear from the list of projects and become inaccessible from Jenkins, just like how it goes when a project is deleted, with one difference — instead of getting deleted, the data is archived into a zip file and stored on the server. This allows the administrator to resurrect it later (aka unshelving), in an unlikely event that the job turned out to be necessary.