/ad'vent/
n. The prototypical computer adventure game, first implemented on the PDP-10 by Will Crowther as an attempt at computer-refereed fantasy gaming, and expanded into a puzzle-oriented game by Don Woods. Now better known as Adventure, but the TOPS-10 operating system permitted only 6-letter filenames.
See also vadding.
This game defined the terse, dryly humorous style now expected in text adventure games, and popularized several tag lines that have become fixtures of hacker-speak: "A huge green fierce snake bars the way!" "I see no X here" (for some noun X). "You are in a maze of twisty little passages, all alike." "You are in a little maze of twisty passages, all different." The magic words xyzzy and plugh also derive from this game.
Crowther, by the way, participated in the exploration of the Mammoth & Flint Ridge cave system; it actually has a Colossal Cave and a Bedquilt as in the game, and the Y2 that also turns up is cavers' jargon for a map reference to a secondary entrance.