Barrier

The Barrier is an invisible block which appears transparent, but does not act as a transparent block. Buttons, redstone, ladders, etc. all can be placed on the block. The block in the player's inventory shows up as a red box with a slash through it (commonly referred to as a "No" sign), but when placed is completely see-through (similar to that of air). Like bedrock, it is indestructible, meaning that it can only be destroyed in Creative mode.

Obtaining
Like Command Blocks, the barrier block is not listed in the Creative inventory, and can only be obtained using external tools or the following command:. Just a note, you can remove the  and use. The barrier block is unobtainable in survival mode without cheats or mods, like command blocks and bedrock.

Trivia

 * Like Bedrock and Command Blocks, barriers cannot be pushed by pistons and can not be destroyed without Creative mode.
 * When you break barriers, lava particles come out.