Quit

The #quit extended command abandons the current game. NetHack will ask you to confirm with [y/n]. Use this when you want to give up on your current game and start a new one with a new character.

Once you quit, there is no way to return to that game unless you are save scumming; if you only want to close your game and resume later, use the save command, Shift + S.

History

In old versions of NetHack, as in Hack, the Shift + Q command would quit. However, this command was rarely used, so newer versions changed Shift + Q to quiver and introduced the extended command "#quit". This is why, on your first use of the quiver command, the game will remind you to use "#quit" to quit.

Encyclopedia entry

Maltar: [...] I remembered a little saying I learned my
          first day at the academy.
Natalie: Yeah, yeah, I know. Winners never quit and quitters
          never win.
 Maltar: What? No! Winners never quit and quitters should
          be cast into the Flaming Pit of Death.

[ Snow Day, directed by Chris Koch,
  written by Will McRobb and Chris Viscardi ]