Standoff markup (sometimes also called “out of line” markup) includes methods that locate at least some markup quite separate from the content it applies to.
The term ‘Standoff Markup’ served within the TEI Council as a rather loose denomination for everything to do with the need to point into some other part of the current or a different document, including out-of-line markup (that is markup that is living outside the document, but using some kind of pointing facility to address locations or spans within the document) via extended pointers and linking.