Purge is a function that is sometimes necessary to use to update a wiki page whenever template- or subpage-transclusions are involved. Purging clears the page's server cache, and the page is rebuilt. Before purging, you may want to try first to refresh the page using your web browser.
For updating a page display, any purge methods do the job, but for categories and backlinks a null edit explained below is required, and other methods don't work. Update of images is explained in a section below.
The page to purge is the one that transcludes, not the page that gets transcluded. Purge consumes a small amount of additional processing power to rebuild the page.