"hack and slash
" based game, of the genre "dungeon crawler". "Hack and slash" denotes oen of the game's requirements: Killing things (monsters, in this case) until you level up enough to continue.
The primary goal of this game is to retrieve the "amulet of Yendor" for your character's god, and after retrieving it (from the deepest level of an extremely large dungeon), carrying it all the way back up and through 5 planes.
The game has multiple thousand references to fantasy books and games, such as "Hack", another "hack and slash game", Lord of the Rings
(a fantasy series by J.R.R Tolkein), and Dungeons and Dragons
Many game completions ("ascensions") require over 12 hours of gameplay, and Nethack is known as one of the most difficult to beat games of all time.