EXPLOSIVE ROUNDS - Volatile payload explodes on impact, dealing a portion of the weapon's damage in an area.
Bullets detonate on in a 2 meter wide radius on impact
In Destiny, EXPLOSIVE ROUNDS is an Ehancement Upgrade that can be found on Rare and Legendary Weapons. Weapons in Destiny pull each Upgrade at random from specific pools (with a few Weapons that are an exception). Explosive rounds give bullets an aoe type damage at the point of impact.