The word "revision" is used in private servers to refer to the version or build number of the game. We associate certain content like skills, minigames and the visual appearance of runescape to a number.
Here are some examples:
#317 - this revision was runescape as it was in 2006. This features a really old looking User Interface (a.k.a gameframe). There are only 20 or so skills. This was just before construction was added to the game, which means it also does not feature Hunter, Summoning and Dungeoneering to mention a few.
474 - released in 2007, this was when the GodWars dungeon was added, with godswords.
508 - the HD graphics update, and bounty hunter crator minigame which replaced the Wilderness
614 - release of dungeoneering in 2011
718 - runescape in 2012
750 and higher - introducted on Evolution of Combat (EOC)