Air

In Minecraft, 'Air' is an invisible, non-solid block that occupies any space not filled by another block. Though technically a block, it's not usually considered one because it has no collision box and cannot be interacted with. Air is unique in that it automatically replaces any removed block, even though it doesn't visually flow. Air is essential to avoid drowning or suffocating from falling sand, gravel, etc. In early versions of the game, air affected horizontally adjacent fluid blocks, causing them to either disappear or spread. There are three types of air: regular air, cave air (found underground in caves and some generated structures, only in Java Edition), and void air (used internally in Java Edition for unloaded chunks and areas outside world height limits). These types of air function the same, differing only in their ID names. Air cannot be created, destroyed, or obtained, even with inventory editors. Air is represented as small blue cubes when 'Show invisible blocks' is enabled in the structure block save mode.