Airburst round

An airburst round is a type of tactical anti-personnel and anti-aircraft explosive ammunition, typically a shell or grenade, that detonates in midair, causing air burst effect fragment damage to enemy personnel or aircraft. In the latter case, airburst rounds are used in anti-aircraft or "zenith" cannon, known in military slang as FLAK or ack-ack.
This makes it easier to hit enemy soldiers behind a wall, in a defensive fighting position, or in a confined space or room. It is used on many guns, from artillery to the hand-held XM25 Individual Airburst Weapon System. Unlike traditional grenades, such as the 40 mm grenade, smart grenades can be electronically programmed to explode after travelling a certain distance. A fire control computer or some other electronic sighting system is used to quickly program the electronic fuse with any distance, as conditions dictate.
Orbital ATK developed 30x173mm Mk310 PABM-T airburst rounds for Mk44 Bushmaster II.

Terminology

It is also called an airburst shell, air burst grenade, programmable ammunition, 3P ammunition or smart grenade.