Web Parts that are available to users at run-time are contained in Web Part galleries.
A Web Part Page gallery contains Web Parts that are already added to the current page. This gallery is different from the other galleries in that it is dynamically generated. It contains Web Parts that are added to the page but are closed (the IsIncluded property is false). The Web Part is still associated with the page by an entry in the SharePoint database, which also stores any shared or personalized property settings for the Web Part. To bring back a closed Web Part, select it from the Web Part Page gallery.