Transclusion

Transclusion is generally the inclusion of the content of a document into another document by reference. In the Wikipedian context, it is the use of the template functionality of MediaWiki to include the same content in multiple documents without having to edit those documents separately.

Examples
Transclusion/How_Transclusion_Works and Template:POTD are transcluded to this page using and.

Template:Flu and text Spanish flu research are transcluded to Spanish flu using "" and "" respectively. Note that transcluding prose in articles is a debated issue. The alternative is to create a short introduction and link to the prose.

Pages related to MediaWiki transclusion
123abc i like pop
 * MediaWiki namespace
 * m:Help:MediaWiki namespace
 * m:Help:Variable
 * Wikipedia talk:Template namespace

Templates
hi my name is bob i like cheese
 * m:Help:Template
 * Template namespace
 * Template messages
 * Template limits
 * Avoid using meta-templates (rejected)