Bedrock is the only material in the game that cannot be mined. It forms the boundaries, bottom, and sides of the map. It can be placed and removed in Creative mode, but it can't be removed by mining in Survival mode. This material is a "protection" for evict falling into "the void".
Bedrock is sometimes dropped by Nethereyes when killed. The bedrock collected can serve as a decorative element. Also, you can make such a house (using bedrock) that is unbreakable. This is good as no mob can break the house. It is bad because once placed, you can never mine bedrock in survival mode.