The description of a plug-in JSPWiki is present at the page JSPWiki Plugin.
The description of a plug-in installation is available on the page Installing Plugins.
The list of the plug-ins included in JSPWiki are listed here: JSPWiki Core Plugins.
The following pages belong to the 'Plugins' category (or link to it for some strange reason) :
AbstractReferralPlugin
ContributedPlugins
Counter
CurrentTimePlugin
Denounce
EncryptPlugin
GoComicsPlugin
GroupsPlugin
HitCountPlugin
IfPlugin
Image
ImageGalleryPlugin
IndexPlugin
InsertPagePlugin
JDBCPlugin
JiraPlugin
ListLocksPlugin
NotePlugin
OutlinePlugin
PageViewPlugin
PanelPlugin
PhotoCollectionPlugin
PluginListPlugin
ProgressBar
RecentChangesPlugin
ReferredPagesPlugin
ReferringPagesPlugin
ReferringUndefinedPagesPlugin
SampleAjaxPlugin
SearchPlugin
SessionsPlugin
TableOfContentsPlugin
TreePlugin
UndefinedPagesPlugin
UnusedPagesPlugin
VideoPlugin
WeblogArchivePlugin
WeblogEntryPlugin
WeblogPlugin
WikiFormsPlugin
WikiPlugin
WorksheetPlugin