An ionic pulse was an energy discharge that could be produced by Galaxy-class starships.
In 2371, when the USS Enterprise-D came under attack from a D12-class Klingon Bird-of-Prey, Lieutenant Commander Data targeted an ionic pulse at the Bird-of-Prey's defective plasma coil. This had the effect of engaging the Klingons' cloaking device and lowering their shields, making them vulnerable to a counterattack. (Star Trek Generations)