A PluginSet is a collection of plugins, represented as an XML file. These XML files can be created from the button of the Manage tab of the Plugin Manager. Saving a PluginSet remembers all of the currently loaded plugins.
When a PluginSet has been saved, it becomes the "default pluginset", which means that if you unload/uninstall plugins from that set and go back to the Install tab, you should see them selected for download again. To clear this setting, click on thebutton in the Install tab.
It is posisble to Choose/Open a PluginSet from the Manage or the Install tab. The behavior of choosing a PluginSet depends on which tab you are on when you choose it. From the Manage tab, it unloads plugins that are loaded but not in the list. From the Install tab, it selects plugins from that list that are not loaded, marking them for download from Plugin Central.
When choosing a PluginSet, the path can be given as a remote URL. This helps teachers and sysadmins direct the students/slaves to a standard set of plugins that are required for the course/job.