"Damage bonus" refers to an extra amount of damage or power that is added to something, like a weapon or an ability. It makes the thing stronger and more effective.
Sentences with «damage bonus»
This would solve the other issue, in that your main character is very weak, gaining damage bonus only with ally crew members. (metacritic.com)
Characters have an innate 50 % bonus to damage when desperate (in addition to any other damage bonus effects they may have). (zeboyd.com)
And if you're able to figure out what enemy is weak against what you can gain elemental damage bonuses. (otakudome.com)