A hypertext system is one for displaying information that contains references (called hyperlinks) to other information on the system, and for easily publishing, updating and searching for the information.
Probably the first description of the idea came in 1945, when Vannevar Bush wrote an article in The Atlantic Monthly called As We May Think, about a futuristic device he called a "Memex". He described the device as electronically linked to a library and able to display books and films from the library, and further able to automatically follow references from these to the work referenced.
Computer scientist Ted Nelson coined the word "hypertext" in 1965. He founded the Xanadu project in 1960 with the goal of creating such a system on a computer network, further documented in his 1974 book Computer Lib / Dream Machines and the 1981 Literary Machines. Nelson's work and many other early hypertext systems such as Douglas Engelbart's "NLS" and the popular HyperCard application bundled with the Apple Macintosh computer were quickly overshadowed by the success of Tim Berners-Lee's World Wide Web, even though the latter lacked many features of those earlier systems such as typed links, transclusion and source tracking.