Air is a "block" in Minecraft. It is the spaces that are not filled with a block, mob, or a object. It is classified as a non-solid block. It has always been in the Minecraft game.

Air is everywhere where a mob, block, or player not is.
Vital statistics
Type Non-Solid Block
Tool N/A
Physics N/A
Blast resistance N/A
First added Classic-Pre 0.0.0
Hex 0
Dex 0 Bin 0000