From Minetest

A block in Minetest
Block Type Gas
Drops Nothing
Physics No
Luminance No
Flammable No
Generated Yes
Renewable Yes
Stackable Yes (99)
Itemstring air
Inventory icon of Air

Air is a transparent node, which can be walked and passed through by players without any resistance. An air node can be destroyed by building a solid node to its position, like for water and lava. When a non-air node gets removed, an air node immediately takes its place.

Fire occasionally replaces air near flammable nodes.

Air is the most common node in Minetest. A large part of the world above sea level consists solely of air. Air is also found underground in the form of caves. Air is one of the nodes which can't be obtained during normal game-play.

The map generator tries to ensure that the player always spawns inside air.

Air is one of the few nodes that are always available (along with Ignore), regardless of which games and mods are activated. If a game does not define any nodes whatsoever, the world will solely consist of air.

The map generator “singlenode” generates a map which consists solely of air, even if games or mods have defined other nodes.