Bedrock

"Bedrock lives at the bottom of the overworld and the top and bottom of the Nether. It was added on the tenth day of Minecraft's development - 20 May 2009 - only three days after the game was released to the public for the first time. It's older than water, lava, ores and logs. But dirt, grass and stone are older still."

- Duncan Geere

Bedrock is a block, indestructible by survival means.

Obtaining
Bedrock cannot be broken using any tools. It also cannot be moved by pistons or destroyed by explosions that are present in survival gameplay. Bedrock can only be obtained by the creative inventory and commands. Even if theoretically broken, bedrock would not drop as an item.

Natural generation
Bedrock comprises the bottom-most 5 layers of the Overworld in a rough pattern, although to the 4th layer is predominantly flat bedrock with only rare gaps, rendering the very bottom 5th layer mostly inaccessible. In the Nether, bedrock comprises both the top and bottom 4 layers in a rough pattern. At the top of the Nether, bedrock prevents the player from going past layer 127. It can also be found at the sides of the Nether.

In the End, individual bedrock blocks make up the natural end crystal structure, and the bedrock remains after the destruction of the crystal. Bedrock additionally forms as part of end gateway portals, created when the dragon is killed, and as part of the bedrock exit portal which is generated at the center of the central End island.

Usage
Bedrock's primary usage is as a solid unbreakable block. It also prevents mob spawns and is the only solid block that beacon beams can shine through.

Additionally, when in the End and set on fire, the fire on bedrock will never go out naturally, similarly to netherrack.

Trivia

 * In the console editions, only the highest layer in the Nether of naturally spawned bedrock is unbreakable.
 * It is possible, but rare, for ore to be found encased in Bedrock.
 * In Minecraft 4k, there is bedrock on the bottom of the map with no texture.
 * Strongholds can cause a bedrock not to form within its bounds.
 * From its addition in classic through some versions of alpha, bedrock's texture file was called Rock.PNG.