Barrier

A barrier is an invisible block which appears transparent, but has mixed properties. All dependent blocks can be placed on a barrier, such as trapdoors or redstone, however, it lets light through and renders adjacent surfaces. 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, barriers are not listed in the Creative inventory, and can only be obtained using the following command:. Just a note, you can remove the  and use. Barriers are unobtainable in survival mode without cheats or mods, like command blocks and bedrock.

Trivia

 * Barriers cannot be pushed by pistons and can not be destroyed without Creative mode.
 * When you break barriers, lava particles come out, like Locked Chests.
 * Unlike Bedrock, Ender Dragons can destroy barriers.
 * A barrier in the inventory is the second block that uses it's respective block ID, but does not display in the inventory as itself (the first being the hopper). Note that this is unlike similar blocks, such as the cauldron, that use a seperate item ID.