Transclusion

Transclusion means that a thing can be in two places at once.

The MediaWiki parser processes an article in two stages. The first stage is called preprocessing and is mainly involved with the transclusion of templates and the expansion of the Wikitext.

Transclusion has always been a key component of the vision of hypermedia, ever since its earliest days (Nelson 1965). The term was originally used to denote the inclusion, by referential addressing, of part of one document within another; […]

Directives that use transclusion are treated specially by the compiler in that the contents of the directive's elements are removed and provided via a transclusion function before their compile function is called.