According to the Wikipedia, Memex is:
[...] the name of the hypothetical proto-hypertext system that Vannevar Bush described in his 1945 The Atlantic Monthly article "As We May Think". Bush envisioned the memex as a device in which individuals would compress and store all of their books, records, and communications, "mechanized so that it may be consulted with exceeding speed and flexibility." The memex would provide an "enlarged intimate supplement to one's memory". The concept of the memex influenced the development of early hypertext systems (eventually leading to the creation of the World Wide Web) and personal knowledge base software. The hypothetical implementation depicted by Bush for the purpose of concrete illustration was based upon a document bookmark list of static microfilm pages, and lacked a true hypertext system where parts of pages would have internal structure beyond the common textual format, so it's fair to say that early electronic hypertext systems were inspired by memex rather than modelled directly upon it.