From the introduction:
What Is This?
Dungeon World is a roleplaying game that uses sweet modern roleplaying techniques to create an old school adventure game feel.
The cool modern ideas are mostly from Apocalypse World, D. Vincent Baker’s game of a post-apocalyptic wasteland. The rollicking adventure feel is taken from editions of Dungeons and Dragons from Advanced Dungeons and Dragons through 4th Edition. Together, they make for a fast, fun, driven fantasy adventure game.
The first Apocalypse World/Dungeons and Dragons hybrid was Tony Dowler’s Apocalypse D&D. This is a continuation of Tony’s great ideas to a bigger game.
This isn’t the full Dungeon World game. Dungeon World is a complete game, [while] Dungeon World Hack requires Apocalypse World to play it.