Definition of "transclusion"

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

1990 September, Ted Nelson, “On the Xanadu Project”, in Byte, volume 15, number 9, page 298

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.

2011, Hannes Dohrn, Dirk Riehle, “Design and implementation of the Sweble Wikitext parser: unlocking the structured data of Wikipedia”, in Proceedings of the 7th International Symposium on Wikis and Open Collaboration (WikiSym '11)‎, Mountain View, California: Association for Computing Machinery, pages 72–81

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; […]

2012, Julie A. Jacko, editor, Human Computer Interaction Handbook, 3rd edition, CRC Press, page 571

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.

2014, Brad Dayley, Learning AngularJS, Addison-Wesley Professional, page 229