Bedrock

Bedrock is an indestructible (except in creative mode) block.

Obtaining
Bedrock cannot be broken using any tools. It also cannot be moved by pistons or destroyed by explosions that are present in normal gameplay. Bedrock can only be obtained by the creative inventory and commands.

Natural generation
Bedrock comprises the bottom-most 5 layers of the Overworld in a rough pattern, although to the 4th layer is predominately flat bedrock with no gaps, which makes the very bottom 5th layer 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 console edition. Bedrock in the Overworld and the Nether always generates in the same pattern no matter what seed is used.

In the End, defeating the Ender Dragon spawns a portal with a bedrock frame. A single piece of flaming bedrock also appears underneath the ender crystals. As of 1.9, bedrock forms as part of the end gateway portal, created when the dragon is killed.

Usage
Bedrock's primary usage is as a solid unbreakable block. It also prevents mob spawns and is the only solid block that beacons 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 lowest layer (and highest 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.