Bouncing Effect refers to an exception in combat where an individual ship's attack is less than 1% of the shield power of a given defender. When this happens, the attack is "bounced off" the shielding (hence the name) and nothing happens. This is most often noticed when Light Fighters are attacking a Large Shield Dome, but in theory can occur with any ship or defense as long as the prerequisites of the effect are met.
When this takes place, the attacking ships will be unable to cause damage to the enemy they are fighting. In the above example, the Light Fighters will never be able to kill a single Large Shield Dome without support, even if there are 50,000 fighters to one dome, unless the attacker's weapons technology is 11 or more levels higher than the defender's shielding technology.