Border

Border blocks are unbreakable blocks that prohibit movement through, over or under them. They are exclusive to the Education Edition.

Usage
The border blocks are generally used to prevent students from entering a specific area. It can only be placed or destroyed by a player that has a permission as a world builder.

It emits a red particles. When placed, the block collision will prevent the non-world builder player from getting through or placing a block, above and under the border block infinitely.

Trivia

 * Border blocks and cobblestone walls share the same block models and inventory model.

Reference
Bordure Border 边界