"The hole" is another phrase used to describe solitary confinement in a jail. This is a bit of older prison lingo used back when it was legal for a prisoner to be thrown into a dungeon-like room for an arbitrary amount of time. Living there is difficult as there is no light, no toilet, and just a floor to sleep on.
You always here "the hole" used in prison movies like The Shawshank Redemption, or any movie that takes place on Alcatraz.