Hypertext
Also: hypermedia, Ted Nelson, Xanadu
Ted Nelson's name for non-linear, linked writing — text that branches and connects the way thought does.
Hypertext — a word coined by Ted Nelson around 1965 — is writing that isn't confined to a single sequence. Documents link to documents; readers choose paths; ideas connect to ideas directly rather than through the bottleneck of the page. Nelson's larger system, Project Xanadu, imagined two-way links, version tracking, and transclusion (quoting that stays connected to its source).
Nelson's roots run back to Vannevar Bush's memex, and forward, in diluted form, to the World Wide Web — which kept one-way links and dropped much of Nelson's vision (he has been pointedly unimpressed by the result). His 1974 book Computer Lib / Dream Machines remains a manifesto for the personal, liberating computer.
Hypertext is one of the purest tools-for-thought ideas: the structure of the medium made to match the structure of association.