Hypertext is text that contains links to other text, allowing a reader to move between documents in an order of their choosing rather than the order in which they were written. The term was coined by Ted Nelson in 1965.
A printed book supports one primary reading order, with footnotes, indexes and cross-references as devices for escaping it. Hypertext makes the escape the normal case: any point in a document can lead directly to any other, and a reader's path becomes an individual route through a network of material rather than a position in a queue.
This changes how documents are written. A hypertext article can assume that any term a reader does not know is one click from an explanation, so it need not define everything or repeat background. The cost is that authors lose control of the order in which their material is met, and each page has to make sense to someone arriving from anywhere.
In "As We May Think" (1945), Vannevar Bush described a hypothetical desk-sized device, the memex, that would store a person's books and records on microfilm and let them build associative trails between items: permanent links, followed at a keystroke, that could be named, saved and passed to a colleague.[1] Bush's argument was that indexing by category fights the way memory actually works, which is by association.
Ted Nelson coined the words hypertext and hypermedia in 1965 and spent decades on Project Xanadu, a design in which links were two-way and visible from both ends, documents kept every version, and quotations were transclusions of the original rather than copies, so that a passage's source was always traceable and its author automatically credited. Xanadu was never completed. Nelson has been a consistent critic of the World Wide Web for discarding these properties.
Douglas Engelbart's oN-Line System, demonstrated in 1968 in a session later called "the mother of all demos", showed hypertext links, the mouse, video conferencing and collaborative editing, all working together. Apple's HyperCard (1987) put linked stacks of cards on ordinary desktop machines and introduced a large number of people to authoring hypertext.
These systems shared an assumption the Web abandoned: that the material being linked is under one authority, so links can be kept consistent. The Web's one-way, unchecked link works precisely because it demands nothing of the far end.
Every hyperlink on the Web is an instance of the idea, but so are the cross-references in a wiki, which push it further than most: on a wiki, a link may point to a page that does not exist yet, turning the link into a request for someone to write it.