date directive is supplied by the date plugin.
This directive can be used to display a date on a page, using the same display method that is used to display the modification date in the page footer, and other dates in the wiki. This can be useful for consistency of display, or if you want to embed parseable dates into the page source.
For example, an update to a page with an embedded date stamp could look like:
Updated [[!date "Wed, 25 Nov 2009 01:11:55 -0500"]]: mumble mumble