Air

Air is an invisible, non-solid block that occupies any space not filled with another block.

Overview

Air cannot be created, destroyed, or obtained, even with an inventory editor. Although it is technically a block, it's usually not seen as such, as there is no way to interact with it because it has no collision box. Air is unique in the way that it automatically replaces any block that is removed, even though it doesn't visually flow. Air is required to avoid drowning from water, or suffocation from falling sand/gravel/concrete powder.

Background

In the Indev versions, air affected fluid blocks that were horizontally adjacent to it. If the air was touching a fluid block, there was a 2 out of 3 chance the fluid block would disappear and make the pool recede and a 1 out of 3 chance the fluid block would fill the air, making the pool spread. 

Trivia

• Air is programmed to fill any adjacent blocks that are not already full. Sometimes, there is a glitch where a player takes suffocation damage when blocking water, or emptying the block of anything other than air that the player is standing in.
• Even though air is nonexistent in the Void, a player does not suffocate. They are just unable to place blocks beneath the bedrock level.
• In Alpha/Beta/release 1.3, players could have the air block in their inventory.
• Air is one of the four types of blocks generated in all three Minecraft dimensions, the other being bedrock, chests and obsidian (1.16+ only).
• Air is the most common and oldest block in Minecraft.

Blocks
Natural	Air • Stone • Granite • Andesite • Diorite • Bedrock • Clay ( Terracotta) • Cobblestone ( Moss) • Cobweb • Dirt • Gravel • Coarse Dirt • Bone • Ice ( Packed • Blue) • Spawner • Sand ( Red) • Sandstone ( Red) • Obsidian ( Crying) • Snow • Sponge • Wet Sponge • Stone Bricks ( Cracked • Mossy • Chiseled) • Prismarine ( Dark • Brick) • Sea Lantern • Pumpkin • Bee Nest • Grass Path • Infested Block • Snowier Snow </td> </tr>
Manufactured	Bookshelf • Bricks • Wool ( Carpet) • Concrete( Powder) • Conduit • Dried Kelp Block • Fence • Glass ( Pane) • Stained Glass ( Pane) • Glazed Terracotta • Hay Bale • Iron Bars • Jack o' Lantern • Ladder • Painting • Scaffolding • Slab • Smooth Stone • Cut Sandstone • Smooth Quartz • Smooth Red Sandstone • Slime • Snow • Stairs • Walls • Wood Planks • Wood • Beehive • Honey Block • Honeycomb Block • Polished Diorite • Polished Granite • Polished Andesite • Red Nether Brick • Quartz Bricks • Polished Blackstone </td> </tr>
Ore	Coal Ore • Diamond Ore • Emerald Ore • Gold Ore ( Nether) • Iron Ore • Lapis Lazuli Ore • Redstone Ore • Ruby Ore • Nether Quartz Ore • Ancient Debris </td> </tr>
Mineral Blocks	Block of Diamond • Block of Emerald • Block of Gold • Block of Iron • Lapis Lazuli Block • Block of Quartz • Block of Redstone • Block of Coal • Block of Netherite • Block of Ruby </td> </tr>
Utility	Bed • Brewing Stand • Cake • Cauldron • Chest • Shulker Box • Crafting Table • Enchantment Table • Furnace • Jukebox • TNT • Anvil • Blast Furnace • Barrel • Bell • Campfire • Cartography Table • Composter • Fletching Table • Grindstone • Lantern • Lectern • Loom • Smithing Table • Smoker • Stonecutter • Target • Respawn Anchor • Lodestone </td> </tr>
Redstone/Travel	Button • Dispenser • Redstone Lamp • Door • Fence Gate • Lever • Note Block • Piston ( Sticky) • Pressure Plate • Rail ( Powered • Detector • Activator) • Redstone ( Wire • Torch • Repeater • Comparator) • Trapdoor ( Iron Trapdoor) • Trapped Chest • Hopper • Dropper • Daylight Detector • Tripwire Hook • Observer • Redstone Ore • Block of Redstone </td> </tr>
Plants	Cactus • Dead Bush • Chorus Plant • Flowers • Wither Rose • Grass( Grass • Fern) • Leaves • Lily Pad • Melon • Mushrooms( Huge)  • Mycelium • Podzol • Nylium • Pumpkin • Saplings • Sugar Cane • Vines • Cocoa Pods • Wheat • Log • Corals • Kelp • Sweet Berry Bush • Nether Roots • Fungus • Weeping Vines • Twisting Vines Sea Pickle </td> </tr>
Liquids	Lava • Water </td> </tr>
Non-Solid	Fire ( Soul Fire) • Sign • Torch ( Soul) • Banner </td> </tr>
The Nether	Glowstone • Shroomlight • Netherrack • Nylium • Nether Brick ( Cracked • Chiseled • Fence) • Nether Quartz • Nether Gold • Ancient Debris • Nether Wart • Nether Roots • Weeping Vines • Twisting Vines • Fungus • Soul Sand • Soul Soil • Basalt • Magma Block • Blackstone </td> </tr>
The End	Dragon Egg • End Stone • Purpur( Pillar) • Endstone Brick • End Rod • Dragon Head • Ender Crystal </td> </tr>
Creative only	Barrier • Structure Block • Jigsaw • Command Block ( Repeating • Chain) </td> </tr>
Bedrock Edition only	Stonecutter (old) • Nether Reactor • Light Block • Glowing Obsidian </td> </tr>
Unused	Locked Chest </td> </tr>
Removed	Cog • Dirt Slab • Cyan Flower • Camera(BE) • Wax Block </td> </tr>
Unimplemented	Crying Obsidian (old) • Wax Block </td> </tr>
Education Edition only	Element Constructor • Material Reducer • Compound Creator • Hardened Glass • Border • Underwater TNT </td> </tr> </table> </div>