Help:Transclusion

Transclusion is the process of include the content of a page in another page, by reference rather than by copying and pasting it. Templates are usually transcluded into pages : the template text exists once, and is editable in a single place. It is added to pages where it appears when the page is loaded.

You can transclude any page on the wiki, like so:

  {{welcome}}  will transclude the template [[Template:Welcome]] where it is placed in the page
  {{:welcome}} will transclude the page [[Welcome]] where it is placed

For more, see m:Help:Transclusion on the Meta-Wiki.