Air-Blast

An air-blast (abbreviation: AB) is the Pyro's primary weapon's secondary attack. It can be activated by pressing the right-mouse button when the Pyro's primary weapon is equipped (with exception to the Phlogistinator which has no ability to air-blast).

Air-blasts can reflect projectiles coming towards the player. Such projectiles include rockets, grenades (from the Demoman's Grenade Launcher), arrows (from the Sniper's Huntsman), balls (from the Scout's Sandman), and juices (Sniper's Jarate and Scout's Mad Milk).

In TFDB, air-blasts are used to reflect rockets and nukes.

Other Abilities
In some servers, the air-blast can be used to throw opponents into the air. This can cause distractions and/or making their enemies more vulnerable to getting hit by the rockets. It can also be used to throw players into pits or any other environmental dangers, leading to an environmental kill.

Often times, such air-blasting is considered a cheap method of play and hence, some servers do not support it. Hence, these air-blasts are strictly towards reflecting rockets and nukes only.