Lihzahrd Bricks make up the structure of the Jungle Temple. They are the toughest block in the game, being impervious to explosives and only breakable using the Picksaw or a better pickaxe or drill. They also cannot be made inactive using actuators until Plantera has been defeated, unless they are above the world's surface.
Like jungle grass, placing 80 / 140 Lihzahrd Bricks in one area creates an artificial Jungle biome. This is not useful for growing jungle plants or spawning jungle monsters, as both require the grass, but makes setting up enemy drop farms easier once the Picksaw has been secured, as one does not need to wait for grass to spread and the introduction of the Jungle biome will generally increase spawn rates.