Bedrock is a form of material at the bottom of the world. The bedrock of the Magic Kingdom is said to be especially hard. Ordinary Dirtamancy is unable to manipulate it, but this can still be done with a Dirtamancy/Carnymancy caster link, though that still requires a considerable amount of juice.
Barring high level Carnymancy, bedrock physically cannot exist outside its natural layer. Even though the Wonky Wrench is able to remove it and add it, it is never collected in the process.Hvs.tCF 274
Real World References
See the bedrock Wikipedia article.
In Minecraft, the bottom of the world is composed of bedrock blocks, which are normally impossible to penetrate. It is however possible to place and destroy them in creative mode, which allows the player to use any block. Breaking past them leads to an endless void.