This number tells how much damage the aircraft does by firing each of its weapons until they are empty and need to reload. If the aircraft has a squadron size larger than one, the number is multiplied by the number of planes in the squadron.
If the weapon can do critical damage, the number includes the average added damage from the critical hit, depending on the critical damage chance of the weapon. A critical hit adds 50% of the normal damage on top of the regular damage.
The burst damage value is a theoretical maximum and the actual amount of damage is less because of factors like enemy flares and air defense.