Minecraft wiki entry for Block_update, associated text: A block update is an in-game mechanism that occurs when a block is modified in some way. Limited to the computing power of a computer, the game can not process all blocks at all times, which is why the game needs a mechanism such as a block update. When a block changes (due to a player, an entity, or a chunk tick, etc.), it notifies nearby blocks that they should check if they need to respond to the change.