The Pit of Hyuna, also commonly refferenced as "The Pit", is a giant hole in the End that leads to the Void. It was named after one of the first Netherans who first fell in by accident.
The Pit of Hyuna is named after the infamous Netheran Hyuna Irahdo who wanted to explore the End, only to be knocked in by an Ender Dragon. The Pit was created when Scourge was a teen-dragon from a falling meteor that crashed into a weak patch of End Stone. Rather than exploding, the meteor crash-landed into the ground and tore a giant hole straight through the End Stone and falling into the Void. This re-awakened several underground End monsters, who dug through the ground and emerged in the bottom of the hole, some falling into the Void.
At that point, the Ender-ground monsters were wakened from a long hibernation and learned to eat whatever fell in. This included some Endermen, Non-End dwelling monsters, and even several dragons. It is now used as a form of punishment among the Herobrinians, whom throw in whoever disobeyes Herobrine.