For efficiency in service, MediaWikicaches pages. Depending on the exact sequence of actions editors follow, one may view an out-of-date version of a given page. This happens most often on heavily-edited pages and on pages which contain an instance of transclusion.
{{purge}} adds to any page a link that, when clicked, not only reloads the page, but clears the server cache, forcing the page to be completely rendered "from scratch". This is not a one-time solution; generally, editing a page is itself sufficient to purge cache. Rather, it is a measure taken in anticipation of the frequent need to purge.
