Bedrock isfound at the bottom of every world and lines The Nether. It is an indestructible block when trying to mine it. In Creative Mode, it is available as a building block.
Access to the Void, the area behind Bedrock, is impossible in the Overworld or the Nether, as the bottom layer of bedrock is unbreakable even in creative mode. However, layers above this can be broken. This means the void can only be entered in the End.